Sorry, there are thousands of varieties of named peonies and probably way more than that of unregistered seedlings, makes it really hard to be 100% sure with NOIDs. I'd start with determining some other things about your plant--size, whether it's fragrant or not and take pictures of the foliage as well. You also need to determine when it blooms in the peony season--early, mid or late. The University of Michigan has a historic peony garden and has pictures of several hundred historic varieties, you might want to start there to see if you can match it. Here's their website http://peony.mbgna.umich.edu/database/peony-database  Yours is a really pretty flower, I don't think I have anything that looks exactly like it so can't give any leads. Hopefully you'll have some luck on UofM's site.

very unusual flower!

Beautiful bouquet! Like Liz says, it is really hard to id pink and white double peonies.

I love it and I love that it was your grandmother's. I have one of my grandmother's peonies, too. Very special. Even if you don't know the variety you can call it your grandmother's name for fun! That is one beautiful double peony, too. Congrats!

My money's on festiva maxima. The white one with dark pink middle thingees in your photo is what you'll see if you google. But mine is planted between two dark pink bomb peonies, and it blooms just like your photo: the earlier blooms are light pink. (No clue if the reason is the dark pink neighbors. Maybe it's common in f.m.) anyway I'm no expert but thought I'd mention that. Oh and F.M. has been around since the mid 1800's so definitely could be from grandma's garden.