Why would she stalk my friend on socials

I’ll keep it short, dated this girl for a while. Something happened in her life and she started pulling back, I tried to support her but she eventually stopped replying to my texts. I sent the last text a few days ago but started moving on after texting twice with no reply.
I go to events with my friend who is a woman and we tag each other in stuff on instagram. Last night my friend called me and said the girl I was dating was watching all of her stories, and they don’t follow each other or know each other. I just don’t understand why she would be doing this?