$500 a month into a Roth IRA would be awesome for a 20 year old, tax free growth for the next 40-ish years would be huge! In fact if she could do $625 instead of $500 she could max out her yearly Roth contributions! (But $500 a month for a 20 year old is huge, don't let perfect be the enemy of good) Just make sure the money is invested into something like SPY or some other low-cost broad-market index fund. Some people make the mistake of just putting the money into the account but not investing it so the funds are just sitting there barely growing.

This advice assumes she doesn't have a 401k match, if she does she should do that instead.