Oh she 100% gives it all to her parents so they don't ever have to worry about expenses ever again. They are a humble family that has had to make difficult choices and unconventional living arrangements, so that would be her way of giving them a break so they can do whatever they want

Elio has enough wealth to last him the rest of his life, so he'll most likely invest it in a business venture, and when it turns a major profit, will donate 75% to various charities and charitable projects... because he can.