I have name-changed just in case something gets back to someone...
My SIL (DH's sis) is in her late 50s and hasn't been able to have children, though she desperately wanted to. There are lots of other significant ways in which her life hasn't worked out for her, and she lives alone in a small village not a million miles away from us.
When I first gave birth to my DD, my DH asked me to let SIL look after DD from time to time because she doesn't have kids of her own. At the time I felt uncomfortable about this because (1) I didn't quite know what he was asking of me - it sounded almost as if I was being asked to 'share' my child; (2) I felt as though there was subtle (though unintended) pressure from somewhere but couldn't quite put my finger on it. I was, understandably, caught up with looking after my new child and my new role as a mother, so I ignored these feelings, and have let SIL have days out with DD. However, sincen day 1 I have observed a sort of possessiveness from SIL towards DD. I thought that perhaps I was imagining it, until two friends separately confirmed that they had noticed the same thing as well.
In addition to this SIL has tried to accuse me of maltreating her emotionally, in a number of ways. To cut things short, she was describing someone else, not me - which has been verified by my close friends and DH. It is quite clear that her accusations are all about her feelings about the 'failures' in her own life, but that she needs to deal with them properly, not try to push the blame onto someone else. At the time I wish I'd said this more explicitly, but you can hardly say: 'You're just saying that because you haven't got children and I have', now, can you?
Anyway since that big blow-up, she thinks everything is resolved (because I failed to stand up for myself fully - bloody fool that I am), whereas I am finding it really difficult to see her. I feel resentful towards her and paranoid about any communication with her because she misinterprets stuff at the drop of a hat. I haven't stopped her from seeing DD, and would never try to, but I just am not happy to be around her at the mo. I am expecting another DD in a few weeks and she's already started talking about taking both of the children 'to give me a break' - she always talks about wanting to give me a break, rather than talking about her own needs. Now I do not doubt that she genuinely does want to help me, but I would also like her to be honest about her own feelings so that we can operate on an open footing. I don't expect that it will ever be easy to balance this relationship, but until we start talking honestly I think it will always be much more strained than it needs to be.
Oh, and another part of the problem is that she pulls up the defences big time when you try to talk about stuff that affects her (when you start to speak she bulldozes over you with verbal diarrhoea - like saying 'nuh nuh nuh I can't hear you'). So even though I know we need to talk, how the hell can we?