Opinions/

IDK where to even post this, but wanna know if my feelings are right or if I'm over reacting. Me and my SIL are friends, no hard feelings just because she is an "in law". She has two little girls by my brother, 2.5 and 1yr+3 months. We have a bouncer that is literally brand new. We have it set up for the baby already. I don't want other kids playing with it, I don't want it tore up. Well, my niece, who is one, loves it.. I just feel she is way too big to be sitting in it. My SIL, instead of telling her to stop and trying to get her to understand it isn't hers to play with (I don't want her spanked or something that extreme), she tells me that if I don't want the things in my house broke or tore up by her kids.. than they should be put up. I haven't went off and she was nice about it, but why am I being obvious about not wanting this played with and she continues to watch her kid on it and I'm the one who has to pick her kid off of it and I need to put things up in my house so that she can come over? Maybe I'm just hormonal though.