Kaja I always appreciate your perspective, but I think you are oversimplifying.
My only and older brother had a problem keeping his penis in his pants and I'm sure that my parents would have liked a Chastity belt to help keep it where it belongs. He was lucky in that he didn't end up becoming a daddy at 17 or 18 only because his pregnant girlfriend happened to become impregnated by someone else.
That being said he also only dated age appropriate women who were apart of his social circle. Jane doesn't have the sense to do that so this goes well beyond a normal or healthy relationship. It's easy to simplify this as 'Jane is a slut', but that's not really the issue at hand, it's more about her inability to do anything but find toxic relationships.
A Chastity belt seems like it would be a good solution in that it doesn't prevent her from engaging in the things she enjoys compared to her parents not letting her go out at all. The belt protects Jane while keeping away toxic men who are only interested in Jane as an object.
My advice wasn't meant as 'Jane is a slut', she shouldn't be allowed to have an orgasm, it is more about it you are going to wear a chastity belt it needs to be on by default so that you build up confidence wearing it so that it is there when you need it. I'm sure Monica wouldn't have a problem with Jane having some alone time, the idea is more about changing the mindset from "you need to be punished if you want to engage in these activities" to "do you think that this activity is a good reason not to wear protection?".