I have a friend who takes Prozac (also known as Fluoxetine) for depression who has recently gotten very into psychoactives.

I'm honestly worried about her drug use, but that is neither here nor there. She has her heart set on taking Ketamine, and I'm worried that it will adversely interact with the SSRI medication.
I did a little research and couldn't find anything definite on interactions. Is there anything definite out there?

I've told her I'm worried about her use, but there's no way I can stop her, so I'm trying to at least help her be as safe as possible.

I know we're not supposed to talk about illegal, habit-forming substances, but I am not coming out in favor of it at all, I'm just trying to get advice to help my friend, and you all seemed like the most trustworthy people to go to.

No MAOI, this is sometimes used in accompaniment with psychedelics in order to get a more intense effect. It is used with DMT in a mixture of ayahuasca and sometimes it is smoked. Common MAOIs are Syrian rue and harmalas. Also if she isn't finding releif from her depression make sure she knows that psychedelics amplify current emotional states. If she is suicidal DO NOT let her trip alone as she may realize something so horrible that she acts on impulse.

Ketamine is known to help stop depression almost immediately, because of this it is VERY addictive to some.

Theres no nasty interaction with ketamine and fluoxetine pharmacologically speaking; the advisability of taking ketamine when requiring antidepressant therapy could be inadvisable in some cases, depending on their psychiatric history/current state.