Hi,
I'm a trainee film and media teacher, who has a degree in film and did both BTEC and A-Level Media, Film Studies and was heavily involved with performing arts.
From my experience, if she isn't going to go into a performing arts career then I wouldn't do it at college as it is extremely demanding (most of my friends did/do it and it ended up being their only subject), but she can still take part, which from experience is better as you get all the fun stuff without the grading and pressure! What she could do is enquire as to whether they run a production arts course alongside performing arts, I have friends who have done this and are going on to be stage managers and have went to the country's best arts university. A course like this will allow her to discover how a stage production works, how to do lighting and sound and how to direct, which works brilliantly alongside media and a media career.
For the media course, let her decide which one she'd prefer. I did both, and I performed better in the BTEC because I work better in coursework graded projects, which are demanding but you can steadily work towards your grade, and in the a-level my being bad at exams let me down, I got a Distinction in BTEC (which is the BTEC equivalent to an A) and I got a B in A-Level, so it's really about how she is graded best.
For a course alongside, either Film Studies or English Literature are best, or if she's interested, politics. Film with Media will lead to a very creative pathway and university course, so English Lit if she enjoys it might be safe as it means she can always go into teaching.
University wise, as long as she puts the work in, she should get in! Both BTEC and A - Level offer something called UCAS points, and these points all add up, so if she talks to her tutors she can find a suitable university to aim for, but I got into two universities and a teaching course with a Distinction, B, B, and a D, so she shouldn't worry too much!
If you need more help please give me a PM