Difficulty between my 26 year old daughter and her grandmother.?

Here's the problem. My mother spoiled my daughter with gifts mostly . No discipline from day one. Told her from the time she was probably 4 that she was the only grandchild even though there are several other grandchildren. Now it has come back to haunt my mother since her grandson has moved in with her for financial reasons. So my mother gives him attention and this hurts my daughter like nothing else. She is spoiled rotten by her grandmother no doubt. But its getting to the point where my daughter is absolutely furious about this and goes crazy when she hears about her cousin getting something or my mother feeling sorry for him.

I just don't know how to handle this. I told my mother 22 years ago she was creating a monster by saying the things she said and giving into and buying what ever my daughter wanted. Leaving the mess for me and my husband to clean up.

I know this will end badly since my mother is almost 80. But I don't know what to do .