Personally, I would view this as a huge glaring red flag, an almost certain dive into unhealthy territory.
I can see why you'd say that... .where is the line between "relating to each other's painful experience" vs. "becoming each other's amateur therapist". Friends care for each other, including consoling when times are tough, but this was a virtual stranger who began venting her life story basically. I like to think if it was me, and someone I've seen around but didn't know well asked me if something was wrong, I would say "I just broke up with someone and I'm still hurting. He did and said some cruel things to me when our relationship ended, and I feel really out of sorts, like I've lost my sense of myself. Just really fragile. Thanks for asking." But it didn't sound like this woman had the self awareness to say something like that (hence the "you're not saying I'm crazy" response.)
In a way I think it's good that she ran into rarsweet and not someone else without knowledge of this type of relationship... .otherwise she might well have left the interaction thinking that she was crazy (or almost as bad, someone who would label the ex as a creep with no further introspection). The question is, will she be able to recommend books, professional resources etc. to this woman, then she goes and uses them and reports back on how things are going... .or will this woman latch on, trying to get her to meet all those needs for her. There will probably be a need to set some boundaries.
For myself anyways, (even though I would have politely interrupted to make an interpretation or summary much sooner than 30 minutes) my tendency is "I would want someone to listen to me if I was in distress, so listening to others is the right thing to do." Which is ok, but did I check in with myself whether, in that moment, I felt ready and available and "grounded" enough to listen to this person without costing myself? As in, was it an authentic response coming from my true feelings, or was it a rationalized "should"?
