I don't think it is. Usually, such titles are often used for fictional works that draw inspiration from various sources but aren't based on actual events. This could be a case of that.
I'm not sure specifically which 'girl under the bridge' true story you're referring to. There could be many stories with such a title. It might be about a girl who has an encounter, perhaps a difficult situation like being homeless or in distress, under a bridge.
The location under the bridge could be a place of isolation. It might signify that the girl is in a marginalized situation, away from the normal hustle and bustle of society.
I'm not sure which specific 'girl under bridge' true story you are referring to. There could be many such stories. Maybe it's about a girl who was found under a bridge in a particular situation, like she was lost or in distress.
One interpretation could be that the girl was a runaway and the bridge was her hiding place from whatever she was running from, such as an unhappy home situation.
The song 'Under the Bridge' by Red Hot Chili Peppers was inspired by Anthony Kiedis' real - life experiences. He was struggling with drug addiction at the time. The 'under the bridge' referred to a place in Los Angeles where he used to go to get away from his problems and think. It was a very personal and emotional song for him.