Sounds like it could be angina, despite apparent youth. I'm not overweight or a heavy drinker/smoker but suffered a heart attack three years ago, aged 36. I'm only here today thanks to having a mate who is a paramedic and who was on duty conveniently close at the time. I was 'dead' for three minutes and so, so lucky. Looking back it was obvious I had suffered angina for weeks previously but it never entered my mind at the time - because of my age I just presumed I'd become unfit . Hopefully this is summat else but please do make sure she gets it checked out. She's nowt to lose but a couple of minutes with the doc.