been a Vanguard customer for 30+ years and if you are asking about safety, the risk is almost nil. Even when Lehman went down and many MMF’s went under $1.00 par, the parents bailed them out. Even teh Lehman customers got most of their money back.
Question(s): how old is your kid? Do you need the money next year or in 5+ years? Are you in a high tax state and tax bracket? Is the money in your name or hers?
If yours and high tax bracket, I’d look to a short or medium term municipal bond fund which is tax exempt.