It would help to know the LAC. If you aren’t comfortable sharing that, what proportion of matriculating students submitted test scores per the most recent CDS? Do you know if the LAC has a do no harm policy with regard to test scores?
With that said, I don’t think there are many schools where the math score would be ‘held against her’, again she will be evaluated in the context of her school cohort. If she doesn’t submit, the risk is that schools may assume she has a lower score than she does…and her score in context of the HS is very strong.