I'm not interested in getting in a debate, but bipolar is not chronic depression by a long shot. Bipolar used to be called manic depression, so maybe you mis-typed.

People with bipolar have to very careful with any form of antidepressant medication because it can shoot them straight into a manic state - whether or not that includes psychosis.

The trick is to give the bipolar patient enough medication to keep them out of their low spot without sending them off the deep end into mania - it can be a very delicate balancing act.

I'm no expert on THC & it's effects on depression. I just wanted to share my first-hand experience with THC with someone in a somewhat manic/psychotic state that many doctors would classify as bipolar just so people would be aware. It's well-established (I think NORML even has something on their site) that anyone with a psychotic disorder including Bipolar I must be very careful about using any form of marijuana.

Don't get me wrong - I'm extremely pro-MMJ & advocate for it at every turn, but, like all medicines, THC isn't for everyone.

That's not to say it won't help the OP's sister - if she only suffers from depression, it very well could. And if it does, it would be so much better than everything else she's tried.