Having an Oxbridge degree won't make the difference to her career options. It is not a golden ticket.
She needs to choose the course and the university that best suit her.
Employability isn't just about the degree. The thing that got my my foot in the door was related to software experience I had through my summer job in an office, not my degree. The thing that made me realise my chosen career path existed was through the volunteering I did at university, which also gave me the experiences that proved I could do the jobs I applied for.
My family members and friends who studied at Oxford weren't able to work during term time (my part time job at my Russel Group Uni was brilliant).
I'm still glad I did the degree in the arts subjects I chose because that is what interested me and that's what I wanted to learn more about. University is about learning, it's about analysing and researching, it's purpose isn't solely about employability.
Please don't make her do a STEM subject if that's not what she's interested in. I'm not even clear from your post what she wants to do the most.
What sector does she want to work in? What are her passions and interests? I know so many successful, satisfied professionals who use their creativity and compassion to run huge businesses, organisations, trusts, charities, theatres, touring producing companies, all sorts, and they've got arts degrees or humanities degrees.
Of course, if she wants to do STEM subjects, that's fine but she might end up like my friends who felt pressured into doing that and have ended up retraining and working in completely different sectors but starting from scratch as older adults.
How old is she? I'm guessing these are decisions she's of an age to be making this year? The Oxbridge decision needs making earlier because of the timings of applications and interviews so maybe it's that pressure that's putting her off too. I'd say the subject is more important to nail down than the uni because if she's a high achiever, that should dictate which unis are the strongest in that field.
My son's just finished A levels and he was keen to avoid the debt of uni so he prioritised looking for degree apprenticeships, industry placements, funded fees etc. But he also knew which industry he wanted to work in and that's shaped all of his choices from there.