They're a bit different but they carry very similar meanings. I changed it to malgastado. Gastar can also mean malgastar sometimes, depending on the context. I think in this context in can work, as it's clear that she didn't get any results in her 'investment' and thus the spenditure was a waste. But since malgastar also carries that meaning and doesn't lend itself to ambiguity, I put it like that. :) Thanks for your observations.