I highly doubt that OP’s D will get kicked out of school for this, or worse (like being jailed).
OP has been played, because he trusted his ex-wife and wanted the best for his D.
I agree that a lawyer should be consulted, in order to protect OP from making this even more of a mess, and to prove good faith effort at resolving a situation where he reasonably suspects fraud has occurred, and that he is arguably tied up in.
Ultimately, I think the School FA office will need to be consulted, and with an attorney’s assistance, an equitable resolution can be found. They may simply start with an audit of OP’s D’s historical financial aid application records, and if things do not look as clean and proper as they should, they may take further action. Penalties theoretically may involve a revocation of aid granted fraudulently, which may end up resulting in them preventing OP’s D from registering for classes in her senior year until the situation is resolved, but I don’t think it gets that far that fast. This probably drags out longer than that, and I would even suspect that they may find that OP’s ex didn’t contribute her fair share of 50% (according to the agreement she had with OP). It doesn’t sound like the ex will be able to convince anyone that she didn’t know what she was doing, this is soo confusing, etc. but it would not surprise me if she tried.
Like it or not, the OP’s D is in a messy situation - she is also the one who should be getting an attorney. She is the one who filed, based on what her mom told her, and probably said she lived with her dad who she apparently has little contact with.
OP should let his D know he reasonably suspects that fraudulent activity has occurred, and that he is in the process of obtaining legal assistance. He should recommends that she retain counsel to protect herself as well, as he believes he is obligated to report this lest it continue, which might make him appear complicit. Once OP and his D have both found counsel, the counsel would best determine if and how they report this to the school.
OP is generally responsible for anything he signed, but at this stage, if fraud has occurred, his ex instead might be responsible for any loans she signed pretending to be him.
Please let us know how this plays out.