I agree it was none of her business! Too many mothers try to get involved (interfere IMO)in their adult child's marriage. My MIL would look in my closets to see if I was a good housekeeper, really made me mad. But she was 45 when the son was born and women didn't work out side of the home and their 'job' was to keep a clean house. I can't imagine asking my daughter if my 15 & 17 yo grand girls are still virgins. She is your daughter and your responsibility not the MILs!
When my 17yo visited with her boyfriend THEY brought up the conversation that her dad did not trust them to be alone. And then, and only then, I told them they were too young for sex, IMO, and she stated in front of him that she wanted to wait for marriage. Now saying and doing are 2 different things lol!!!!
I think I would have been upset too, it must appear to your daughter that they were talking about her behind her back like she was a baby not a teenager.
In the MIL's defense (if there is one lol) she grew up in a much different time. I am 58 and we were not told anything about sex. The attitude was girls were to be virgins until marriage, and being 'pure' meant you didn't know anything until the marriage bed. Boys were expected to 'sow their wild oaks' and that would help them settle down and be faithful to their wives. Big laugh right lol!!!! If you are close to your MIL, and she is close to the daughter, you might mention to MIL that she overheard the conversation and it hurt her feelings. I think you are right and I also would not let it fester into a BIG problem. How old is the MIL????? She could have really asked out of concern, but I would not have liked it either.
AND my sister was a single parent, close to her daughter, and she was crushed when the 18yo went to a doc for birth control without discussing it with her. I told her I was glad she was that responsible. I just don't see how a child can come in and say to their parents they want to have sex lol!!! The first thing I would have done is try to talk them out of it and they knew it lol!!!!

Thanks for the response,rosajoe.
I'm not sure how old MIL is,but I imagine in her sixties.
She is not close to my daughter at all,which is why I found it so strange.
I use the term grandmother loosely,because she has never acted like a grandmother to my daughter.My daughter has never even spent the night at her house.
My daughter very much did feel like they were talking behind her back.

I have always been pretty open with my daughter about sex(without being too graphic).
But I have told her when the time comes if she does decide to do it, that all she has to do is talk to me and I will help her get birth control.But needless to say,her and her father do not talk about those kinds of things!

I do feel that MIL tries to get involved in too many things that don't concern her.Such as asking about our finances and such too.I told husband that he should not answer her questions and that those things are private.

My daughter told me she doesn't really want to go to MIL's house anymore now.She felt like it was a judgement against her by MIL to ask that instead of just concern.

I think it is so sad that some grandparents miss out on their grands life, by choice. But I did know people that had no contact with the grands, they said they had raised their kids and were passed that stage.

I used to tell my daughter I loved them coming and going lol!!! To me, the grands were an extension of the people I love very much. I'm older and had more money so we enjoyed trips and sewing, quilting, cooking. Now they are teens and are too busy for much more than a quick note and a few minutes on the phone. They grow up lol!!!!!

I would not try to get her to visit either. I can understand her feelings of judgement. Maybe the grandmother will notice and ask why, maybe not.

My MIL taught me a big lesson, and that was too stay out of my children's marriage. Abuse is a different story!

It is also your husbands job to say something to his mother, 'cause if you do it may really make her mad!

The teen years are hard enough! At least your daughter talked to you about. That is a huge positive!!

At your age I may have thought differently, but at my age now, it's not worth it. Just keep the lines open with your hubby and daughter. And just let the rest go!!

Just look at it as it gave you the opportunity to discuss sex with your teen lol!!!!!!!

Very upsetting for your daughter to hear that conversation and very inappropriate conversation to bring up with her son. Why would she even ask, presumably they don't talk on that level, usually ?

I think the issue is if you and your hubbie are united in the way that you are going to answer such probing questions in the future.

Has you husband actually voiced his objection to such questioning ? He needs to say to his mother that he does not feel the need to discuss such issues with his mother.

I think the father and grandma should apologize to your daughter. Hearing something like that would stay with her for life, seeing she sounds like a sensitive soul. It could even make her feel that sex is something to be ashamed of, you never know how these comments affect such an impressionable age.

I love the "sow their wild oats". My thought is who are they supposed to sow them with? Hookers maybe????? LOL

Are you sure its just an issue because its you MIL,How would you feel If It was your own mother asking that question?.If it were my mother asking ,It wouldnt bother me atall,If It were my MIL I would be thinking dont be so nosey,depends on how close a family people are I think.

I can understand, obviously, that your daughter would be upset to have overheard that comment--whether or not she's started having sex yet. From that point of view, MIL was definitely wrong to say something behind your DD's back, but when she could possibly overhear it.

But I'm sort of with Tracy on this. You've got a mom and son who have the kind of relationship where they feel comfortable talking about anything. That's really a good thing, when you come right down to it. It's the kind of relationship we all strive to have with our parents and our children. I'm sure YOU hope that your children will always be close enough to YOU to talk about anything, anything at all. I know, my dd and I can--and yes we even discuss sex, sometimes in detail (she's grown, of course).

Now, as a teacher and parent, myself, there IS a part of your post that really concerns me. You describe a young girl who sounds a bit withdrawn, possibly unhealthily so. Is protecting her from the world at large the best way to handle that? Is she going to be prepared to live in the real world without you running interference when she's grown? What are you doing now to give her the confidence and and courage to get out there and live life, rather than hiding from it? If she is as terribly 'shy' as you indicate, it's time to address that--get her involved in some community activities that will help her develop her interests. Extra curricular activities at school, if there's anything she'd enjoy. Some children don't feel that comfortable with their peers--maybe she'd blossom if she had the chance to: work with the animals at the local shelter; or to volunteer at a hospital, senior center or nursing home; or at the local Ronald McDonald House or library, or a daycare center. Perhaps classes in a creative outlet--drawing, dance would be more her cup of tea. Perhaps an activity that the family can do together--like raising Seeing Eye Puppies (that was one of the BEST activities we enjoyed--the entire family was involved in the whole process, including the monthly 4-H meetings and all their activities).

Please, I beg you because I care so deeply about children, forget putting your energies into hating your MIL over this, and redirect them to helping your daughter learn to be happy and confident, so she doesn't have to hide at home.

Azzalea is right, I would be concerned if my 14 year old grandaughter "hardly ever left the house" I suppose Gramma's question was clumsy but I guess she was wondering why the girl is so shy and not terribly social.