I come from a family of academics. They work bloody hard fwiw and put in loads of extra hours, so they do really need to love their subjects... and she doesn't seem to be that interested at the moment.
The thing is, lots of "exciting" jobs come with loads of stress and long hours, so there are usually compromises to be made of one sort or another. And as someone with an Oxbridge degree and a masters, I can assure you that some of my previous jobs have actually been pretty mundane too!
It is a bit disrespectful of her to keep banging on about how mundane your job is. That can't be very nice for you, even if she doesn't mean to be rude. I would be having words about that tbh. I'm a CEO, and the administrators in my organisation do an immensely important job without which the organisation wouldn't function properly at all.
In one way or another, she needs to understand that nothing gets handed to you on a plate, you have to work for it. Even the "mundane" jobs that she is turning her nose up to, to be frank. I'm not sure how you can get that through to her though.
Can you look at some university websites with her and help her research the entry requirements for a maths degree?