I don't remember mentioning only she can use it ... only that it's rare to use it, because it's not a well understood type of magic. During the conversation, you mentioned several times you need to understand how a certain type of magic works in order to use it effectively. So my reasoning why she can understand it easier is because of a genetic mutation that is carried down her (and some other) bloodlines and become activated seemingly randomly. Basically, it just wires your brain differently in a way so you can understand this type of magic. Yes, anyone is techincally capable, but it takes a certain way of thinking ... like yes, everyone can do mathematics physics, but certain people (like a genius) can more easily understand how to do it.

And... for the connection... I wasn't aware that was a requirement... but she is set up that she can easily start off anywhere. It's not a stretch to say she's be hired to guard one of the nobles maybe (who's not overtly evil, obviously).