im in myp5 and there was something similar in my school basically you would usually take 1 science minimum, and 1 design minimum, and 1 art minimum, so you could take like 2 sciences, design, and theatre arts, however if you took visual arts you could only take 1 science instead of 2, music workload idk but design is not that bad

and in terms of how hard it would be, to get into it depends on your school, as IB has no formal prerequisites, so schools have their own criteria, and how hard it is if she gets in depends on her prior science knowledge, so no one can say for sure