"Don't play more than 2 minions" was for the strat where you force her board to be full of 1attack minions and do nothing but stall with healing/freeze/armor until you can Alex + burst her down.
Which is really quite effective. Maexxna has no face nukes and Hero Powers before doing anything else, so you just need to be able to heal for 7 each turn in order to sustain indefinitely. Putting a third minion down, however, means Maexxna starts sac'ing her weenie spiders and laying out rough shit like Sea Giants.