Suggest to your girlfriend that she consider therapy. Medication could really help her with the mood swings associated with bipolar disorder but as you said, she will not stay on the medication. Maybe if she found a therapist whom she likes and trusts, with his or her help, she may be able to stabilize. You can suggest this to your girlfriend but she may not take your advice.
It seems like she is replacing one unhealthy behavior with another. She went from drinking to obsessively exercising. She is rationalizing the excessive exercising by saying “at least I am not drinking.” She is right in one respect. It is good that she is not drinking but exercising two to three times a day is most likely a sign of mania or OCD, as you mentioned. (OCD can co-occur with bipolar disorder but many of her symptoms may also be mania.)
Clearly she is in need of help. She is currently not stable and may be heading toward an episode.
My advice is this: ask her if she will consider therapy. If she is reluctant, offer to go to therapy with her, for couples therapy. Maybe she’ll go if you are willing to go as well. Also, offer to go to the doctor with her. Monitor her care if you can and try to enforce the doctor’s treatment instructions. If you become more involved in her care, she might be more willing to follow the doctor’s orders.
But also realize that there may be little that you can do. You cannot force anyone to go to treatment or take medication no matter how much you believe or know that he or she could benefit from such care.
People with bipolar disorder and schizophrenia often have difficulty recognizing the need for treatment. Family members often have to battle with their mentally ill family members in order to convince them to take the needed medication or follow the prescribed treatment plan.
You might also want to visit the National Alliance of the Mentally Ill (NAMI) website. NAMI is a national advocacy group that helps and supports families dealing with many of the same issues you are facing with your girlfriend.
I wish you luck. Please write again if you have any further questions.