Maybe I’m being dense but I don’t understand the last sentence. Double depositing doesn’t hurt a school’s bottom line assuming they have eager students happy to come off the waitlist late - something I’ve certainly seen happen - and gives the schools some more petty cash by keeping the non-refundable deposit. It does harm the person on the waitlist who knows they have it as their first choice and keeps them in uncertainty longer.
(Your daughter may be blasé about being on the waitlist but not all are. Plenty other threads on cc to attest to that.)