Understand she knows I was working and wasn't stalking her/them. I've made no attempts to contact her. She knows if this relationship didn't work out, I would only be up for a friendship and nothing romantic with her.
Yes, I'm over-thinking it, but I need a female perspective on her odd behavior.
Most Helpful Girl
There are a few reasons to explain her reaction considering what you've typed.
It could be that someone is feeding some nonsense in her head that you've become a stalker. Maybe she's immature about seeing you when she's with this new guy. 5 years is a long time. Anyone would feel like it's wrong or weird being with someone else when the one you were so intimate with for so long is in sight.
I believe you should ignore it; shrug it off. If she or the new guy has something to say about it, they will. As long as you aren't doing anything wrong, not standing around "looking" stalker-ish. Also, if you were to react to this or question it, the guy or her can easily put it out of proportion and blow up on you. Leave it be.