Kael could do absolutely anything. Technically, Reven could control her in any way he wanted. Perhaps this is less dangerous for the character herself, because suicide involving the guardians is an unlikely outcome for such mind control, but an unknown factor is always scarier than a specific mechanic. And it would most likely affect other players, not Kael herself. If Reven started raining fireballs in the middle of a battle with a dirigible, while I was trying to study him and throwing Carnelian at him, it wouldn't be good for anyone.
Kael could do absolutely anything. Technically, Reven could control her in any way he wanted. Perhaps this is less dangerous for the character herself, because suicide involving the guardians is an unlikely outcome for such mind control, but an unknown factor is always scarier than a specific mechanic. And it would most likely affect other players, not Kael herself. If Reven started raining fireballs in the middle of a battle with a dirigible, while I was trying to study him and throwing Carnelian at him, it wouldn't be good for anyone.