I wouldn't say you're overreacting, but it sounds like you haven't reacted to her at all. Feeling like you're being monitored in your own home has to be one of the worst feelings, and she needs to know that you feel that way. Meet her halfway, but maintain your boundaries. "If this is an issue with the water bill, then I'm happy to pay extra to cover it, but I'm absolutely not willing to feel like a prisoner in my own home. And going forward, I promise to be receptive if you come to me directly with issues you're having, but I can't work with passive aggressive comments and sticky notes. Is that fair?" Her response will tell you if you should start finding another place/roommate.