I have been sitting watching this thread and eventually had to pipe up twistella. When I started teaching 20 years ago, all PE teachers taught another subject (usually badly, as their degree wasn't in it and they had perhaps an A Level to maybe not a very high standard in it so they ended up with rotten classes!). The history teachers I know who teach politics are using skills and knowledge of history to research enough and know enough to teach it. It is still an uncommon A Level so they are not falling back on politics A Level and degree knowledge : likewise, quite a lot of history teachers have politics etc degrees. I have taught 4 A levels in my time , all related to my degree but only one of them contains contents of my degree and/or my A Levels. I have also taught German with just an A level (and German Lit at uni...). But teaching a second subject has become LESS common, not more (disclaimer : unless DD wandres into the time warp that is a middle school!). People in my school do it if they want to, as much as anything. PE at schools has really diversified in the last 10 years and , as you say, is not just one subject any more . There is core PE, GCSE PE, Sport, various BTecs - and most teachers teach PSHE so not sure why that was even mentioned. I am not a primary teacher but, if I were, I'd be so insulted by these threads that say : ' what you want to do, the thing you have a passion for, is useless... why not try primary teaching?'. Do we want primary schools stuffed with peeople who didn't really want to teach primary (or teach at all)? Any, anyway, primary is also NOT shortage!
Don't let her be put off teaching. Yes, it can be shit (so can lots of jobs). But she wants to do it and it reamins necessary to have a degree to do it , as you say!. I am delighted to hear this as teaching wants and needs teachers who are committed to the profession not people who fall into it because of a bursary being waved at them, for example.
Surveys have shown that PE teachers (and some other subjects) buck the trend for teacher dissatisfaction and are usually at least content with their jobs besides which, every teacher knows PE teachers are over promoted in schools and she'll be an assistant head before she knows it
Good Luck to your DD. I only wish my similar ability DS had half the ambition instead of lolloping about on his backside pretending the future does not happen.