His ex is stalking me??

So recently my boyfriend’s ex girlfriend followed me on instagram. I have so many people on my ig that sometimes I don’t even notice who’s following me but recently my bf was on my ig and asked me why this girl was following me. And I obviously didn’t know that girl he asked me about was one of his exes back in HS. I honestly do not remember ever letting her follow me. But it’s so weird because I notice she is always the first few ppl to watch my ig stories. She doesn’t like any of my posts but never misses a story. I noticed we don’t even have mutual friends on instagram so I don’t even know how th she found me. Btw ladies I am not blocking or unfollowing her because I am not giving her the satisfaction of feeling like she has me pressed 🙅🏻‍♀️ but anyways has anyone ever had their bf’s ex girl stalk you on social media? If so how did you handle it?