My SO [27m] of 3yrs and I [32f] found out another girl [23f] has an Instagram account full of posts about my SO.

This might be a little long and all over the place, but I'll try to make it make sense.

When I first met my SO, he was casually chatting with a few other people and feeling out possible relationships. We ended up clicking really well and started dating.

One of these people he was chatting with, we'll call Jane. He and Jane chatted on and off after we started dating, but he was very open about it (I have a bit of trust issues) and on his side, it was strictly friendly.

Unfortunately Jane is a younger, and slightly socially awkward person. After finding out he was in a relationship she joked about friending me on Facebook. I'm super private with my FB and I don't like a ton of people being part of that. He mentioned that to her and suggested she leave me alone. She agreed and passed it off as a joke. Well wouldn't you know it, that night she added me, and told me not to worry or feel threatened with her and my SO. I shared all this with him and he was less than impressed. He spoke to her about boundaries and not listening to his wishes. She apologised but was very unconvincing with her explanation.

Over the next few months Jane's messages and actions were increasingly concerning. At one point my SO and I talked about how I was getting uncomfortable with her and that I felt that he needed to very clearly set boundaries with her or it was going to keep getting worse. He felt I was over-reacting and assured me she was harmless. Eventually I just asked him to just stop telling me about her messages.

Jane then shows up at my work. She tells me she just wanted to talk and get to know the person her favourite guy friend was dating. I politely, but very quickly found an excuse to hide in my office to get away from her. I'm uncomfortable talking to her, especially in my work place where I need to be professional and polite at all times. I let a co-worker know the coles notes and she watches Jane wonder around a bit and let's me know when she finally leaves. At this point my SO is finally seeing that this might not be as harmless as he thought. He decides to have a brutally honest conversation with her and eventually blocked her number and on all social media. There were a few small incidents afterwards but it very shortly petered out.

Fast forward 2 years to yesterday. I posted a silly picture on IG and got a notice a few hours later that someone I didn't know liked it and immediately unliked it. So of course I creeped them. It's Jane! Well that's slightly unnerving... I showed my SO who has zero understanding of how IG works and tells me 'so what, it's not like she is stalking you. I'm sure she just searched one of your obnoxious hash things.' I was less than convinced so I tried to creep her account, and suddenly I'm blocked. I search her user name and another site shows the pictures she's posted. There are multiple screen shots of conversations with my SO and several of his pictures.

The screen shot convos are all 2+ years old but she has cropped out all of the time stamps to make them all look recent. She also has posted birthday wishes every year to him and calls him her best guy friend and has even made a #instagramless[SOs name] hashtag for all of his posts. We're both super creeped out at this point and have no idea how to react.

We're concerned that contacting her will just be enabling her, but neither of us are comfortable doing nothing. Any advice would be appreciated.

TL;DR - young girl has an obsessive IG account about her and my SO after being blocked by him for years. Secretly stalks my IG and accidentally likes a post revealing it all.

EDIT: Thank you all for your advice, I'm reading every comment and it's all been very helpful. We've both locked down all social media and blocked her on as meant as possible. I got a few screen shots of her IG posts before she blocked me. I've also spoken to my boss about the situation and he's being very supportive.