Talking to strangers is hard

Today I was sitting on the bus, and a young woman was sitting in front of me. She had her hair in a rather strange hairstyle: her hair was divided in about 15 parts and each one was put up in a tiny bun.

At some point she noticed that one of the buns on the back of her head was seriously and apparently painfully messed up, its rubber band stuck where it was not supposed to, and tried to untangle it. She obviously couldn't see what she was doing, and was doing it by ripping as hard as she could and hoping it works. It was quite painful to watch.

I considered giving her a hand, since the whole thing was right in front of my nose, and I could easily do it with much less pain for both parties. Except that, how do you offer help to a total stranger with something like that without feeling totally embarassed? I wished she asked for help.

She did get it done by herself, with a lot of pain and hair-ripping, and then I realized that it would probably have been even more embarassing for her to ask a total stranger for help.

There should be some generally accepted way to ask/offer/decline help in such situations without everyone feeling like a total ass. Or maybe there is, but I just don't know it.