A low dose has anti-depressive effects, but these are much larger doses. According to her husband she was addicted, and on Erowid there are reports of people getting addicted to it: https://www.erowid.org/experiences/subs/exp_Ketamine_Addicti...

Regarding suicide people could get strange ideas due to ketamine, perhaps it's accidental death - perhaps she wanted to try the biggest dose to get the ultimate revelation and while being in the so called K-hole, the cold got her.

Like a few unlucky souls experimenting with psychedelics, they want to fly to close to the sun and fall down. Zoe7.

Ketamine or psychedelic use can be a form of self-medication. But you'd think that if she had depression it was written about after her death or mentioned in one of her books or articles