Always treat her like she is single.
This is super crazy but that girl sounds like one I know in my area. Same thing. 18, boyfriend, hangs with family. Is your girl a pilot by any chance too lololol???
Anyway, the girl sounds super sheltered. IF the boyfriendis a pushover, she may just like him a lot. I don't think a relationship between a 17 and 18 year old could be considered strong. Also if they live apart, I'm sure he is doing other girls.
She may also be very shy about bringing boys around hee family. So maybe that's why she can't hang out. As in she needs a good excuse to see you and doesn't want the family to know. In that case, you should def try to meet her in a place where there is no indication that something is happening between you two... The mall, a museum or amusement park... Anything that she can tell the parents she is going to check out with her girlfriends and not be discovered.
A PU artist leaves a girl better than when he found her so you need to make her comfortable with the fact that you wont get her in trouble with the parents by knowing her boundaries. The best way to do that if you can is to meet them while they are with her. So you can do some comfort on the parents ("you raised daughter well" "hard to be parents nowadays" etc). But be careful how you introduce yourself. You are 22 so they will he skeptical about your intentions. Say your a friend from school or whatever. No not "friend" lol. Just say you have classes with her once in awhile. With parents you must show no intention to get with the girl. Just casual friendship.
Not sure about this strategy but it sounds like it may work for this girl if she is sheltered