First of all, well done to her. She has a nice style, and I think she throws a really nice ball. If she keeps it up, she's going to be fantastic.
As for the double arm swing, what's wrong with it? I do it myself - I don't do it because I was taught to, it just feels natural to let my arm swing.
As for her high series being 645 - big deal. Her average is 171, that's a good bit higher than her average! Many people have high games, and not so high series to go with them.
I think well done to her, and hopefully she will keep it up and get her first 700 soon!