I agree with MLC, Steve and Neffer. Just be very brief and don't offer explanations. Steve's suggested response is on target. No anger or resentment or anything, just plain and matter-of-fact. Then if she sends a nastygram, offer some validation like Neffer said, but also make it clear to her you will not tolerate disrespectful comments from her (if it comes to that). I think now you know why she's been nicer lately, she knew she was going to need something from you.
