I agree with Wild Coyote: it's not a symptom of Bipolar Disorder. This is more of an 'emotional' problem, than a 'mood problem' (see my link to the article on the difference between BPD and BD; I'm not saying she has BPD at all, but I think it's useful to take the advice of the writer of that article and differentiate between what is 'emotional' and what is based on mood).

I've known lots of people who project, and none of them, to my knowledge, has BP. My mother does it A LOT and I try to gently remind of her of this, not using the word 'projection' so she can accept my words more easily. Gentle reminders that she is talking about how she feels, not others, may be helpful. Or ask her, how do you feel? I think therapy would help, where a good therapist would challenge and hopefully begin to heal this very unhelpful habit.