Weird sister in law?

So I live in a huge household and my s/o and I live in the back house and everyone else lives inside the house. My s/o has a brother and his girlfriend and their son in one room. His sister and her family in another and etc. Since day one his mom told me that my s/o’s brothers gf (let’s call her Stacy) didn’t like me at all. I was confused because I’ve NEVER talked to her before. After some time we eventually moved in with and that’s when things got kind of out of control. Everyone in the house gets along with me well and I hang out with them individually a lot and babysit some of the kids.

However Stacy would NEVER let me get close to her kid/feed them and I’m like okay a lil weird but I get it your kid your rules. But then one day she told my s/o’s mom that I would take the other kids to the bathroom alone and that it should be a cause for concern. Wait what. I’m baffled guys. I have never taken them alone and I would never touch a kid like that. What reason do I have to take kids in the bathroom. If that was the case I’d be on some weird predatory list and I wouldn’t be able to babysit some of my family members. When the mother of the alleged child heard what stacy accused she just laughed because she knew me and that I would never do that.

She would also do weird stuff like tell my so’s mom that I would use the same towel as her s/o when we each have our own towels. I’ve FOUND pepper flakes in my shampoo and I caught it just in time but then caught her using my stuff (let that one go because if she needs it then she needs it). She’s blamed me for going into their room and spilling sauce all over the bed (even though she’s told everyone I’m not “allowed” in the room and that I’m banned. So I never set foot in there. As you can see she’s paranoid as hell). I get weird vibes from her so I stay away from her as much as possible.

She always seemed nice to me and from time to time we would try to bond and then she would tell other people something different about me?? It feels like I’m living with a sneaky snake. I never tell her anything now. I want to tell her well if you think I’m doing these baseless stupid shitty rumors then put up a webcam if not stop spreading weird shit..

Everyone in the house had beef with her at one point but we TRY to get over it because she’s the mother of the child and whenever she and the father fights she takes the child away. The family loves the child so we try to just disregard any sneakiness.

Idk should I sit down and have a talk? I feel like every week she’s trying to start some crazy rumor but to my face she’s all fake. It’s making me angry.