What do you mean by "her" 529 plan ?
Does Dad own a plan on which she is the designated beneficiary OR is this a UTMA / 529 which is her plan and Dad is merely the custodian --or what?
This is a can of worms and the states are divided as to imposing a duty on parents in a divorce to provide for college My state, PA has banned it since about 1995 and I think VA failed to allow it to be tacked on as an added duty a couple of years ago --but you check as to emancipation from CS issues in VA. .
And the aid logic embodied in the FAFSA rules is pretty clear--its the income /assets of the CP and any new spouse she may have that matters as to aid and not the NCP's situation. So if aid is to be an issue --you may need to take a fresh look at a different set of rules. And some possible options to improve the child's aid picture.