Depends how the First Amendment is applied. Had the girl been wearing a "gay pride" t-shirt, no problem. Merry Christmas? Problem.
In my opinion, it isn't a matter of the First Amendment, or any amendment, just that something is needed upon which to hang a case in order to defend traditional American values, because the Left can find multiples of "amendments" that are "violated" by behaving -- and expecting others to behave -- in accordance with them, those aforesaid values, and we're left .... floundering around while our founding documents are used against us.
There oughta be a law .........