I'd definitely recommend getting a credit report (not from the websites that advertise with an insane jingle, but from the actual credit bureaus
you're entitled to a free report). Mine had debt from a relative with a similar name; I was able to get that removed. They will also tell you in more detail what goes in to calculating it.
I agree that it's not perfect, and often very opaque, but you should be able to get some understanding of why she doesn't have good credit.
I've heard that RawTherapee is good, but not quite on the same level.