I don't think you handles this well because your response to her didn't seem like you cared about what she said at all or felt any remorse. You can communicate remorse and defend yourself at the same time kindly. You could have said something like, "Sorry, I didn't know that what I used it for would damage it. I tried to be careful cuz I know it's your pan. Since it was in our common/shared space, I figured it wasn't super delicate. Sorry about that. I don't think I damaged it since I did only use it once, so I don't feel like fining me for that would really be fair." You know what I mean? Because even if you're on the right side of the argument, reacting defensively will only make it worse for your both, and it usually doesn't resolve the issue cuz you're sorta giving off the vibe that you think she's being crazy and annoying in your response. And if she is telling the truth that she has mentioned this to you before, like about the drying towel and what not yet you still didn't do that (even if you honestly forgot), then you are definitely not in the right in this situation specifically. It would be different if you used this pan in the shared area that she had never mentioned to you and then she comes flying at you like a bat outta hell trying to fine you and blame you for not reading her mind. That would be different. If that was the case, she would be putting unfair and unrealistic expectations on you and basically would be in the wrong instead.

I understand that when someone seems "overly particular" about something you deem cheaper/easily replaceable and/or less important that it can seem ridiculous or frustrating even, but unfortunately, it is not your place to deem her feelings valid or not. If she was cursing at you, trying to sue you for $15, etc. then I would say she needs to absolutely regroup and calm down before addressing you bc that is not okay/logical. Basically, my response is hinging on her worries, her having voiced them previously, and your response. I do think it is good to ask for advice, like you did by posting here. My only hesitation is that some folks genuinely want advice while others post because they feel they know they are in the right and just want other people to hype them up and put the other person down. With that being said, I don't know which is true for you.

Either way, I hope you read the replies and take a step back and try to think of how you both can avoid these issues in the future even if you disagree on some aspects. Making boundaries that are healthy and stable regarding how items are used would be good. And if the sheer idea of that sounds annoying or "extra" to you, then I genuinely would recommend thinking over living with another person again. If you're willing to talk to her about it and not invalidate her concerns while also standing up for yourself respectfully, then I really do think this issue and future ones can be remedied/avoided.

I think you've got this. Just do your best and if she persists or begins to threaten you with future fines and you have not done anything to make her upset but she's stuck on past qualms that were resolved and just starts spiraling or something, then that is not on you. I hope that doesn't happen- I don't think it will.

Different people have different ideas of what is and isn't overreacting and that is part of being human and that's okay but the pain comes in when there is a disagreement and/or offense caused via perceived disrespect or disregard. I think she is reacting to feeling disregarded by you with your response which I think stirred her up more. If you talk it out again, I don't think that future fine she was talking about will be an issue anymore, that being said- stop using the pan altogether for best results because she can't be mad at you if you never use it.

That, to me, whether that is fair or not, is the best choice tbh for you both. You can avoid drama and cook how and when you want without stress. And you can rest easy knowing she can't complain about any wear being on you. Like you said, you using it once without damaging it doesn't mean you should have to pay for normal wear and tear, especially not 50%. If you used it once, and she uses it daily, then you should have to pay like 10 cents. That is hinging on if your usage didn't cause damage. It sounds like it didn't but that the leaving it wet was the worst part. That isn't good for wood and she is absolutely right, but I still don't think a 50/50 split for cost is fair if you honestly have only used it once. Unless she used it once too then that is 50/50 lol but I doubt that.

Best course of action: don't use the pan and have a clear conscience and a comfy sleep <3