Hampton Court Palace is lovely. I have been over it a number of times.
I used to read books on the Tudor era by Jean Plaidy, I think she isn't too difficult for a teenager and not too explicit about the details of life in those times. You might want to read one yourself to judge, though!

martinca, Hampton Court is well worth a visit, although, as you probably know much of it was re-built/added to by Christopher Wren a hundred and fifty odd years later. The original Tudor kitchens are still there and the wonderful red brick entrance gateway. Also beautiful laid out gardens down to the River Thames. My husband grew up about a mile from the place and always enjoyed time spent there.
As an introduction to that period of English history I personally wouldn't bother with a novel but would get your granddaughter a copy of The Time Traveller's Guide to Elizabethan England by Ian Mortimer which will provide a good 'overview' of that period, not dates and battles but what people ate, wore, their homes, education, beliefs. It wont be dull and she can dip in and out of it and use it for further reference and maybe later trips/study. You might also enjoy it!
If you are just interested in Henry VIII you could try The Children of Henry VIII by John Guy. Not a long or detailed read but gives you the salient points/characters of that time.
As far as I know there is no sexual content within either book

I don't advise Phillipa Gregory. The only book of hers that I read was wildly inaccurate and pretty sexy.

Girl with a Pearl Earring was by Tracy Chevalier and was about the Dutch painter Vermeer.

Thank you all so very much. I had forgotten Time Traveller's guide.... good idea!