If he wants her to get a high paying job in any field, he needs to inspire her to want to work hard. Why isn't he saying, well, if you want to be an interior designer then you'll need to be able to plan within a budget, and calculate volumes for materials in a given sized space, so you'd better work hard on the maths side. Associate her study with something she finds interesting in that way, and it's an incentive. I home educate my 10 year old at the moment, and that's how I get him to study in a context where there's not the same peer pressure, or authority level (if someone's kids are as scared of them as they are a head teacher, then I'm concerned). It works. It works really, really well.
The reality is that all kids, when older, need to weigh up love of a job, with ability to make a living. His desire for her to be financially secure is understandable, but he does need to consider that she will spend endless hours in work, so enjoying, or at least not hating, that time is also important.
But she's 11. What matters now is that she's interested in something, that she has dreams, and that she's motivated to work. Nothing else really matters, in academic terms. Not at that tender age.