i think she's just lonely and is trying desperately to see if she still "got it" to lure a man - married or not, to her web of desire.
i mean.. i think we all have done something to this extent (or not quite) at some point in our lives.. we can't find "the one" or "mr right" or whatever, and of course.. all the good ones are taken! i've experienced it myself.. having ZERO guys talking to me or whatnot for MONTHS and the instant word spread that I was dating someone, everyone swarmed me. We all (in some way or another) want something or someone we can't have, and it's a game/test to see if we can get it.
After you get it, it's you just let it go cuz you've won and don't need it anymore.
i'm not trying to rationalize what she's doing as right.. because it's still wrong IMO, but i am trying to see where she may be coming from. Hell, I admit i've committed this act too.. but not on married guys.. but on my ex's new bfs or my friends' bf's where i know their relationship is gonna fizzle before it even sizzled. lol. i've never done it to friends that have actually said "I Do" though.