I do not lie. I say things because I am manic and I believe them. I may be delusional. I may be paranoid. I may just plain old be psychotic. But I do not lie as part of my bipolar and it disturbs me to hear symptoms described as lies. Could someone who is bipolar lie, to themself or others? Of course. But not just because of having the disorder. If the thoughts are related to the disorder then they are not "lies" they are part of the illness.

There is also denial which either of both parties can have. Denial makes untrue seem true a lot.

There's no way for us to be in your ex-girlfriend's head but if she is manic then what she says and does is affected by mania. If she isn't it still can be affected by what happens in mania. Or she could be in denial. Or lying to herself. Or lying in general.

I think the only way to know is to talk to her and listen and try to figure it out.