That depends on your comfort level.
The rule is to buy low, sell high - or “buy on bad news, sell on good news”.
Not investing while prices are low (because they could still go lower before they recover), and only investing again AFTER the train has left the station, is how people tend to minimize their return, or worse, are taken to slaughter with the other cattle.
So that’s what the “wisdom” will tell you, but that doesn’t mean that this is something you are comfortable with.
As far as your daughter — yes, hindsight is 2020. A good investment adviser would have told you 2 - 3 years ago to move one or two semesters’s worth of money into low-interest/zero risk money market. This way, if the market continued favorably, you’d dissolve some of the equity holdings - but if the market dipped, you’d start drawing from those money market funds.
Where you are now, it truly is everyone’s guess, whether markets will drop further by year-end, hold, or possibly recover a bit. One factor is, whether your 529 will cover all 4 years? If so, you basically should be making withdrawals each calendar year to coincide with expenses. There is no “catch-up” provision.
But, if you only have 3 years saved for, and know that you’ll be funding a year from “cash”, then the CURRENT year might seem to be a good year to do that and leave the 529 alone until the market has recovered a bit.
In my case, I have left-over 529 money that I’m using for graduate school, but I know that for a year or more, I will have to dip into other savings. So I will let the 529 “simmer” for now. No rush to “sell” while prices are down.