My DD6 and my niece (7) are best friends. We live two streets away from my brother and SIL so our kids have grown up together and have a close bond.
My niece often asks if she can have sleepovers at my house with DD, but SIL always says no. SIL has no problem with hosting the sleepovers at her house though and my DD has stayed over there quite a lot. DD got a huge doll house made for her for her birthday and whilst I was dropping something round to SIL today, my niece asked if she could sleep round so her and DD could play with it. I said I had no problems but she’d have to ask SIL, and SIL said no 
SIL has never allowed me to take niece out with us without her being there, if niece and DD want to play it has to be at SIL’s house otherwise SIL insists on coming to mine too. This is ok but sometimes I have work to do whilst the girls play and I can’t really work and hold a conversation with SIL at the same time.
I just feel a bit hurt that SIL doesn’t think I’m capable of looking after niece, and sad for DD and niece that she’s not allowed to sleepover at mine.
So AIBU?