All kids may like challenges but there can be overwhelming ones. A balance needs to be achieved. All kids like success as well so sometimes backing off to one’s comfort level is a good thing. There are reasons there are cutoffs for some courses. Struggling to keep up/get the A is not as good as slowing down a bit to truly learn the material. Consider that those marginal kids will be at the bottom of the class- perhaps not getting A’s but B’s or even C’s.
So what if she doesn’t finish x++ levels of math? She can learn and retain material to even be a mathematician if that is what she later desires.
See how this summer goes. Use the advice above to have her solidify her knowledge base. If during the course of that she dislikes the subject instead of embracing it you have your placement answer for the lower class. If she is enthusiastic she deserves the opportunity to forge ahead on the fast track. No matter which route she ultimately takes she will be able to succeed in college at any math option she chooses. Her future will NOT be limited by getting into/not getting into a certain math track at her HS.