What does your divorce decree say?
You could argue (which i guess is what you are trying to do) that you should be allowed to cover your share with your kid’s Pell grant, and she should pay her share out of pocket. So unless that’s expressly NOT what is in the divorce papers and how you negotiated paying for college, that could be one way to approach it.
Be prepared for pushback, however. You start down the slippery slope of “kid earned 3K over summer. Is that going towards Mom’s share or Dad’s share?” or “Grandma bought the kid a laptop. Does that reduce Mom’s payment since it’s her mother?” Etc.
Are you getting some type of spousal support as the partner with the lower income?