You had them roll stats? This is Fourth Edition man, POINT BUY!
And if Warlock player is being dumb with her choices, than she's not going to do well, simple as that. I mean, if she's using an Implement she literally can't use (she needs to be able to use staffs as implements in order to get that fire reroll, by the way) than she needs to reread the book. Has she read the book? I find alot of players haven't. They've looked through their class section, they've maybe looked at the skills and feats, but they haven't really read the rules and they certainly haven't read the character creation process rules.
And any player who doesn't have their own dice is not committed the game. I have three in my group who don't have their own dice. One is a bum who won't buy his own. The others, I think, just aren't committed enough to RPGs to get their own dice.