Again, I’ll start with the more likely presumption that both parents want to help their children more than they want to stick it to their ex-spouse. I agree that if one ex-spouse has a good reason to believe that this is not the case, they should be cautious before providing information to the other ex-spouse.
Since OP has suggested that there are 4 children involved, and that her ex-spouse earns 3x or more than she does, she might be able to plug in the numbers based on whatever FA award child is given. With a vague idea of income - she may know the ex-spouse’s occupation and might be able to get a reasonable ballpark of income, but she may not now know about ex-spouse’s new wife’s occupation (if there is one) and any of that side of the family’s assets. But the FA award might help her get a ballpark on that as well.
Too many divorced families don’t plan ahead, nor work together, to determine what simple steps they could take to maximize financial aid. From what the OP has suggested, there is no way her ex-spouse would allow the child to spend 51% of time with her, apparently in fear of having to pay child support.
One question I have, is suppose the child applies for FA this year, using the Dad’s income since she lives with him. Suppose she moves away to her state’s school, a FAFSA only school, and she spends 9 months away from home at college. Then, the following summer, she spends 3 months split between her mom and dad. Let’s suppose it works out to 46 days with her mom, and 45 days with her dad, before returning to school. The next year, could/should she then apply for FA using her mom’s income since she spent more time there than at her dad’s?
The point is, in this case, the Dad’s historical stubbornness has hurt the FA for the first year, but perhaps they can learn from the situation, and with proper planning next year, they can still maximize FA for 3 of the 4 college years.
There are 4 children in this family, so does only the eldest have to spend more time with the mom this year? Does using the mom’s income with only one child work out to less FA than using the Dad’s income with 4 children?
I realize it’s easier to say they should just plan ahead and work together to maximize the children’s FA, than it is to actually do so.