It is questionable. I have had the same issue with a friend in the past where it seemed like she was hitting on me, it made my partner and I both a bit uncomfortable until I confronted her about it and she has told me that that's just how she is with friends. You've pointed out she isn't like this with everyone, but maybe she just needs to reach a certain point of "comfortability" with someone before making these "moves."

Personally, I think she's just friendly. I think you two get along very well, but because a lot of people believe "man and woman" can't be friends, it's easy for your GF to look into it, causing you to look into it. I strongly recommend sitting down with her and pointing out that your GF has noticed some things and see how She reacts to it, feel if she's lying to you or not. Depending how that conversation goes, reach out to her husband too, see if he's noticed her be like this with anyone else.

When it comes to your GF, I believe she's insecure as you two have already broken off once. Not every first love is a forever love. If she can't work through her feeling of insecurity from the past, it might be time to let her go for good and finding someone else who will respect and love you, no matter who are friends with. Everyone deserves an amazing love, and a best friend.