Most Helpful Girl
It has happened to me twice where I've seen ex's and then been friendly and nice only for them to contact me and for me to realize it's over for good. The thing is, when you initially see a ex for the first time, you panic and don't act like your usual self or use usual reasoning. She might have felt panicked and thus decided to just go to the thing she was used to which was being very friendly and wanting to make you and the situation "feel" better by looking interested. She likely went back, thought about it and realized she wasn't acting on how she truly felt and reflected on your relationship. I think you should go NC if she said it's not a good idea. It shows she isn't really in the position to try again.