Like @soozievt I can’t offer percentages, but according to equity stats a rather small percentage of their members book ANY paid weeks in any given year. Our D has earned a living wage solely performing for the past two years, usually with 2-3 month contracts back-to-back, but I don’t presume this will always be the case nor that it is typical.
In my opinion it is never a good idea for parents to raid their retirement funds to pay for their kids’ education, though the new car, new house, dining out and travel funds are another story.