That's very nice of you to pay for her graduate school. Usually parents just pay for undergrad and let the kid pay their own grad school, because often it yields a higher-paying job in the end (physician, dentist, lawyer, scientist, consultant, etc).
I am therefore confused. If you are volunteering to pay for her grad school, then presumably you already have the money. If you don't already have the money, then it seems...odd (at least from a mustachian point of view)...for you to take on her debt.
If you have the money already, then either just pay it each year as tuition is due, or keep the money invested and pay it off at the end if tuition is interest-free until graduation. That way your money pile can keep growing in the meantime.
Am I missing something? Maybe I misunderstood your question?