Just a thought flutter arising out an issue I had with my DiL a few months ago and advice which made me look at the problem from a very different angle....have you tried finding something to praise? Be it ever so little?
It was your post above, about her envying the relationship you have with your own daughter, which made me think again. And look at the problem from a new perspective.
Everyone loves a bit of praise. Without lathering it on perhaps compliment her on her shoes, or a handbag, or her children's behaviour, or a nice cup of tea, or anything. Just dropping the odd word of praise when you can.
Little positive verbal strokes
I suspect you are right when you say the fault lies in the relationship with her own mother, and perhaps you can show her how a relationship could be. Help her relearn behaviour patterns. Enlist your daughter in the strategy if possible. Do the unexpected.
It may not work at first but persevere, after all you will be the loser if things don't improve.
A quote for those blessed with a spouse:



