I've seen this happen a lot. The WAS tests the waters for whatever reason. It may happen often before any possibility of reconciliation. I think the best thing to do is to not contact her (except for business or children) and let her be the one to initiate. You could try inviting her out for coffee or something in a couple of weeks time, but be prepared for rejection. These quiet times is when GAL pays out. You get to still have fun while waiting.
One of the things that my H responded to was that I would not be his friend if we D'ed. He was so shocked that he would lose me completely, except as a co-parent. This was in a conversation brought up by him, so don't go and blab it out, if at all. But, a lot of LBS's wonder this, especially if there is still a good friendship going on, like yours. I decided I could not be his friend, if he left his family and D'ed me. I couldn't be a friend to someone who did that to anyone. This started him thinking. But, of course, we all have to make our own choices based on their own reality, and your children are younger than ours was. Still, this is something to think about --- she might be hoping to have you as a dear friend she can count on and OM as a BF.
Anyway, some thoughts thrown your way.
This is such a difficult time. This is the only reason, really, that I stay on this board --- to TRY and help those through this particular part of the journey (and stay in touch with those who journeyed with me).
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim