in most cases having q slow on the aoe part wouldnt make any difference and in the cases that it would it would leave no counterplay for her enemies. It's mechanics are balanced as they are right now.
Her mana is not an issue right now so changing her passive to offer more mana wont solve anything. Her main issue right now is that she has the weakest max burst of all burst mages. Secondarily she lacks the survivability required to play as she was intended by jumping into the enemy team to shutdown a priority target since the current meta is so damage heavy.
The new mage items are going to be relatively negligible to most burst mages and possibly be a tiny nerf due to shifting of mana and cdr around. DoT mages however are going to see a huge buff.