Read between the lines.
She was fishing for an opportunity for a personal rapprochement. Which probably would have gone one of two ways:
- more of the same, and remaining in contact is a hook to re-engage you, or
- a genuine apology/I get it, or as close as she was capable of, which would suggest she doesn't have closure herself.
All of which is in the "not your problem" category. Unless you, based of your knowledge of the particulars, think there is something there warranting your attention.
If it's something other than a professional connection, I would say no, no no no, nononononono.... Toxic people are maddening, even if they change, it's hard to see it... Avoid the heartburn, plenty of fish in the sea.
The way you asked the question, you really undersold yourself. I thought your response forehead-thumping "what was I thinking" social maladjustment until you mentioned the toxic relationship. There, it was just good boundary setting. I would've just said "thanks" out of general courtesy and then never called.
When you are courteous to another person who may or may not deserve it, that isn't a judgment on them. It's about you and who you are.