Look at the machine bobbin area and see which way the finger goes and match it to the website pics. Easy, peasy:>
I've received two class 15 machines out of time, so yes it does happen. I wouldn't say they are prone to timing issues, but if you've been loved and used for many years your bound to have a grandson play with you and mess up your timing. (you know?;>) hehehe. She can get the bobbin case and then you can attempt the retiming on it? She won't be out much for sure. Though, my local repair store charges $75. Tension and timing issues are different beasts. I don't have a vintage Brother, but I've heard they are nice machines! And of course they tend to appear in all those drool worthy colors.