Basically... just accept her apology but don't change your behaviour. Don't act petty because what good will that do anyone? Just be your normal self. Maybe she did mess it up legit, maybe she was doing something passive-aggressive back in retaliation of your own passive-agressive action. No way to know really

Personally? I wouldn't have even acknowledged that she'd done it. If my mom does something that I think was nice of her - I'll say thank you because I would say thank you to anyone. She obviously likes that - I just pay attention for when it gets turned around into an "I did this for you!!!" when I don't do something else. My mom hasn't really done that but I'd probably at this point go "I didn't know we were trading things". If my mom does something that may or may not be done to intentionally piss me off? I don't give her the satisfaction of seeing me get annoyed