Should I reply to a co-worker's e-mail?

Well, I guess it depends on whether or not this issue is something that needs resolved in order to get work done. If not, I would just completely drop it and ignore what she says on that particular topic. Actually I would try to keep everything completely on a professional level with her from now on. If she starts playing games again, just ignore her. Eventually hopefully she will realize that it doesn't push your ons and that tactic isn't working.