I feel for you completely. Our daughter/step daughter is close to us but her MiL is obsessed with her own son and the children and has been very clever in staying with them a lot and even moving to the same town!
I have been hurt more often than I can count over the past few years by this woman (!) who just takes whatever she wants .... or so it seems to me.
I then read a book, ‘Toxic In laws’, which was discussed on another GN thread and it’s amazing! I am now much more relaxed, don’t try to compete (it’s absolutely NOT a competition) and can see how the types of ‘toxic’ in laws that the author describes (engulfing, controlling, rejecting, abusive or chaotic - or bits of all of these types) can be overcome or ignored. And interesting to consider, as the author suggests, how do the other grandparents view us? Do they see us as a threat because, eg, we have more money, etc? It’s also changed for the better how I feel about some neighbours and work colleagues!
As others have said, be kind, don’t criticise, offer what you can without conditions.
Hopefully it will right itself ?