Hi, I am Bipolar, sometimes you will have to make decisions for her she may not agree with.
She will have very deep low periods
and very high moods
the severity depends on the diagnosis
She is also going to be 'normal' for very long periods of time
It is very possible to have a stable relationship if she is on meds or has coping mechanisms.
If she told you it means she really likes you, take it slow but don't abandon the possibility of a loving relationship because of a treatable illness.