I also considered this:

If I can simply provide proof that the total principal and interest of the promissory note attached to the divorce is greater than what would be paid for the student loan over the same period of time - I wonder if that is grounds for taking her to court on the basis of unjust enrichment.

As you said, I will have to see. Even if it is, I don't know that I can afford it, but since I've still got 4 years of paying the current monthly obligation, maybe it would be worth it, somehow.