I don't think this is something exclusive to JWs. There are lots of inconsiderate or thoughtless people in this world, people often do careless things that aren't meant to hurt anyone. She may have thought the stuff in the cabinet was to be shared with her.
I agree with Anewme, when someone is a guest in your home, they should be treated graciously. We expect them to return that behavior, but sometimes they just don't.
Couldn't you just consider that little bit of lotion a gift to her? Maybe she can't afford to buy it and couldn't resist the temptation to try it but was too embarrassed to ask.
Why not take your mom up on her offer, buy a bottle of the lotion and give it to your house guest next time she comes over. Or just drop it and forgive her indiscretion -- it's only a little bit of lotion, a small gift that might have helped her feel better about herself.
Yes, take your stuff out of the cabinet if you're not willing to share it. You'll save yourself a lot of stress.
willow