Thank you both for your replies. She stopped taking lithium about a month ago, and isnt of yet undertaking any psychotherapy. Her doctor suggested that for a short while she stopped taking her medication to see how she felt, and whether other people noticed a difference. Depending on the results, they were considering moving her onto psychotherapy instead of medication. Both her and her mother agreed to this (She still lives with her parents), and for a week didn't tell anyone, including me, that she had stopped taking medication. When she did tell me, I honestly never noticed a difference in her behavior. If anything she seemed happier because she didn't have to take the medication (She also has annemia and suffers night terrors, so for the past few years she's taken medication for these aswell). Apart from these past few days she doesnt seem to be acting any differently, so I wouldn't put this down to the stopping of her medication.

I've asked her a few times since how she is feeling, and how different she feels now she no longer takes lithium. She told me she no longer has as much going on in her head, and after a discussion she said that she wasn't sure whether she prefered that over having more thoughts in her head whilst on lithium. (To clarify, she's talkative and willing to tell me things when she's not in a depressive phase or upset, but otherwise unless I know exactly what to say [Which is never] she's a closed book.

To an extent I can understand why she might not want to talk to me, as in the past i've sometimes been far from helpful. We have argued many times about this issue, her stance is always that she doesn't tell me things because I 'Dont get it', or that because I dont ask, I don't care. My response has been the same, that if she doesn't tell me anything I wont be able to try and understand or work out what I should be asking.

As for your comment about her cycles, there's not a great deal I can ask I dont think as she has an unclassified type of bipolar, which she explained to me means that her cycles are completely random, and sometimes she doesn't have any depressive or manic phases at all for months, but at the same time can have rapidly changing ones that can vary from day to day. The instance in february is a prime example. She went to sleep seeming 'normal', but within a few hours she'd got herself depressed and ended up self harming during the night, completely out of nowhere.

She hasn't heard anything from her doctor yet regarding therapy, but i've said to her that I'd be more than happy to accompany her to therapy sessions if she wanted me there, but she said she wasn't sure, as she might want some privacy.

The next time we meet up i'll ask her what it is she wants me to do like you recommended, and update you guys with what she said.
I am wondering though, what if she says she doesn't know? Or that there's nothing I can do? It's likely she'll be hiding something if she says either of the two because she almost always does that if there's something up. I ask because if she says she doesn't know i'm back to square one with nowhere to look next