Welcome, @
Lala Land!

I think you're already behaving in a WONDERFUL way by forgiving her and bringing her to a Doctor! Now that her Diagnosis is correct, the BEST thing you can do is just support her, be near her and remind her that you Love Her. Other than that there isn't much else you can do in my opinion because she needs to do the work for herself. It's good that she's taking her Meds, but is she seeing a Therapist as well? I feel like that could help A LOT! If you want to know more about Bipolar so that you'll be able to better recognize her symptoms and eventual episodes she may be having, my advice would be to buy some books and consult the Doctor she's seeing on the matter, possibly together with her if she wants so. Her Doctor certainly knows her Condition much better than anyone else here so that may be a good start and hopefully he'll be able to provide GREAT ADVICE for You as well!

I'd also suggest Couple Counselling if it's necessary, possibly with a Therapist who is ALSO experienced with Bipolar II as well!

Finally, since you're here, it won't hurt you to bring your question to the Bipolar Forums as well:
https://psychcentralforums.com/bipolar/ Many people struggling with Bipolar, many of them also married or currently in a relationship, post there and they're ALL WONDERFUL PEOPLE so it CERTAINLY won't hurt you to try to Post your Concerns there!

KEEP FIGHTING AND KEEP ROCKING, MY AWESOME, DEAR, KIND, SWEET, GENEROUS, WISE AND WONDERFUL FRIEND! Feel free to PM me ANYTIME when you need Advice and Support! I am SURE plenty of others will also GLADLY HELP YOU OUT AS WELL if you just ASK! Please do keep fighting and please do keep rocking as much as you possibly can like you're already WONDERFULLY doing ALL and ENTIRELY BY YOURSELF and ALL and ENTIRELY ON YOUR OWN! Sending many safe, warm hugs to BOTH You and Your Girlfriend, @
Lala Land, Your Family, Your Friends and ALL Of Your Loved Ones who ALSO Love You back as much as YOU LOVE THEM!