At what point does privacy go out the window???

Stepdaughter (14) has had problems in the past (2 years) with talking to strangers (males) online and sharing (not sexual but still borderline inappropriate) pics of herself and sharing personal, private and family information, and getting hugely emotionally attached to these people online. The last time, 1 year ago, the person she was talking to turned out NOT to be an 11 year old boy, but a grown man in Jacksonville, Florida. She hid this for about a year? We took her phone away, a police report was made, an officer was supposed to come talk to her about online safety but never did. Her phone was returned only because she needs to have access to us (step-mom and bio-dad) without her bio-mom's interference (bio-mom would refuse to let her call her dad). Parental safeguards were put in place on her phone, BUT she has another phone over at her bio-mom's and ZERO SUPERVISION and is left alone a lot. Last year, same thing, chatting up someone online and proceeding to fall head over heels. I read all the conversations and could easily tell this person was buttering her up, and mirroring all her thoughts to seem like they were in sync and destined to be together. Stepdaughter panicked about being found out and cut contact for about 7 months but I kept finding notes about how she's so devastated that she let this person go. Then this past month he got in contact with her again and she's head over heels again and wanted him to profess his feelings for her but mad that he hasn't been as responsive as before. 🤨 FYI - none of this she discusses with her friends, myself or dad or her mother. Its like her own little world that she lives in. Her mother, by the way, was a serial online dater who was hellbent on getting married. She used to show stepdaughter pics of men online and ask "what do you think?" and talk about how nice they were and then when things didn't work out, how rotten they were. After 10+ relationships in the last 6 years (half of them moved in and eventually moved out, some even moved in with their kids) she managed to nail one down and marry him last year but its already on the rocks. So back to the first issue.... how much can we limit these online things happening? How much snooping through her phone is too much? Its exhausting finding all this stuff, its so dangerous because she's now talking about meeting up with people. Stepdaughter KNOWS the risks, but without completely cutting her off from technology and making her feel like she's stuck in a jail, how do we navigate this?? And knowing that she has unfettered access to online stuff when she's with her mom (every other week)....