I think it really depends to a degree on your circumstances OP. Sadly we're in a landscape where it's very, very difficult to make a decent living within the creative industries and embarking on any degree has financial consequences.
My friend's DS is not academic but talented at art. He will probably do an art degree - but he's from a very wealthy family. His parents will be able to support his living costs through his degree and, later on, buy a place to live and will no doubt help with living costs if necessary. In his case, it's a 'low risk' option. Such circumstances are not the case for most people - the harsh truth is that most people need to support themselves in the world, and for artists that isn't easy.
There are, of course, a number of vocations beyond an art degree - film/TV, for example. But these are immensely competitive - and an art degree isn't essential, even if you want to go and become a set designer, for example.
A few things to think about - a year-long art foundation courses after school are free, so she could always do that and see how she goes. Also, if she really, really wants to do an art degree but is worried about earning power, remember that paying off student debt is income dependent. Simply put, if she never goes on to earn over a certain amount, she won't need to repay!
Finally, and I mean this kindly OP, an 8 in GCSE art doesn't always equate to an immense talent that must be nurtured at all costs. At my dd's school, pretty much all of them got 8s and 9s at GCSE. A handful of those have gone on to do art A-level (including my dd), but I don't think any of them are planning to embark on a fine art degree - I think they all feel that it's too narrow in terms of future career prospects.