I think I can answer as far as golf is concerned. There are no such things as amateur winnings. If Michelle won the tournament, she might get the trophy but the first prize money goes to whoever comes in second.
The same applies to whatever prize money she is entitled to. It goes to the next winning score.
I remember a story about an amateur in one of the Buick tournaments(they sponsor a couple) a few years back. He got a hole-in-one and won a brand new Buick. He was faced with the prospect of accepting the car and in so doing, declaring himself a professional or declining the car and retaining his amateur status. He accepted the car as he was a college student and had no professional aspirations and it would affect him not at all. He lost his amateur status but drove back to school in a brand new car. Pretty cool!
There’s not much doubt Michelle is going to turn professional and if she was to win a major tournament the temptation to accept would be strong. The prize money on the LPGA is not as high as on the mens tour but not chump change either.
Don’t know about other sports but the principle is probably the same.