Dear Magwhich,
I think it matters how well you know the person to some extent and can see it both ways. On the one hand if you are comfortable enough with someone looking over your place, you would think you trust them implicitely and would not mind if they replace something of little consequence. However having said that, some people are very sensative about thier "things" and I can see that they see that as a violation of trust or something. Of course if you knew the person better you might know thats how they would view that act.
Your right what might not be a big deal to you might be to someone else. It is also a fact that you might not know that the bottle you took or replaced might have had special meaning to that person, special gift from someone, a loved one, so it might not have just been a bottle of rum but something irreplaceable. Although im sure thats not the real issue in this case.
If this person is older, it could be that she is just crabby like some older people get to be. My advise is steer clear of Cat Ladys althogether,,,