Freaking out

Okay so my boyfriend’s grandma babysat my daughter yesterday. Well she’s always saying how it’s stupid small babies can’t drink water and things like that. I told her not to give my baby water, she’s not allowed to have it until a certain age and I don’t want her having it for safety reasons and she said she wouldn’t give her water. I just went to do the dishes and there’s a small bottle with a tiny bit of water in it. I don’t know how it got in there, it was closed and everything, just sitting in the sink and I asked her but I know she’s going to lie about it. I don’t know if she gave her water or even if she did, I don’t know how much she did give her. My baby always gets the hiccups and she’s always like “want a drink of water?” joking around but now I’m thinking it’s not a joke and she just lost all babysitting privileges if she went behind my back and is lying to me. I’m a FTM and a paranoid mess. My baby’s poop has been runnier and she had an upset tummy she said but now I’m thinking she did give her water and it’s messing with her stomach. I thought I made my rules clear and could trust her. Apparently not.

Adding- I know she can have a little bit of water at this stage but her doctor told me to wait till 6 months unless she needed 1-2 oz for constipation right now. She’s never constipated and hasn’t been. And the thing is, is that I don’t know how much water she would’ve given her. She probably wouldn’t give her 1-2 oz. She told me she didn’t give her water and I told her it was okay if it was a little bit but I wish she would’ve told me before doing such. That makes me think she will just do whatever she wants when she wants to so I’m being more strict about it and seeming a little extreme.