A 1550 is phenomenal….if she really gets that. That’s the 99% so I would never assume vs hope. No doubt she’s capable but it’s still…well higher than 99% so I would personally never assume.
But if she’s amazing enough to score there, I would not have my child take the ACT or not prep for it anyway because In almost all cases there’s zero extra benefit. However there are some cases where a 36 could get you more $$ than a 1550. I’m 99.9% sure you are seeking a far more select school but just as an example here is a case where perfect beats near perfect (for auto merit).