Depends how much stress Malfurion is put under. It's heavily implied in WotA that he has such a close bond with the natural world that his power is only limited by the energy he can draw from the planet, and by proxy - the planet's energy is the limit of his magical strength. He is only ever depicted drawing on such extreme strength though when he is under serious emotional turmoil. So just have her kidnap Tyrande or something and he should flip a shit.