You’re obviously aware of their playstyle, and if they aren’t very well versed in the rules, maybe you could roll a couple of melee focused spellcaster (Hexblade Warlock, Bladesinger Wizard, etc) options for them and have them choose from one of them rather than relying on them to come up with something on their own? They’d still have some agency, but would play a character that better suits their playstyle.

Oh, and make sure the options don’t have a dagger in their equipment list. 😄