Mood swings, depression, anxiety, chronic fatigue, sleep walking/talking, grinding teeth, driving sleepiness.. etc all of these things are a sign of a sleep disorder. If your friend has doubts she should get them checked out by a sleep specialist with a pulmonology/nuerology certification.
From what I understand with bipolar, and I don't have it myself though I had an ex-boyfriend with it, during the manic phase, you don't sleep much if any but you still feel very fresh and awake while you are up and you are going, going, going. Now, if you have severe sleep problems and can't fall or stay asleep, you usually feel very tired and exhausted and not at all wired and hyper and go, go, go. There should be other things contributing to a diagnosis of bipolar--possibly low levels of lithium in the blood, cycles of feeling happy & good (with even grandiose schemes--my ex got on a bus for Chicago convinced he would be the next NBA superstar during a manic phase), and low down periods where the person is very depressed and even suicidal.
If she is unconvinced about her diagnosis, she should consult a second psychiatrist and a sleep specialist as well.
I would support thoroughly investigating the possibility of a sleeping disorder. Unlike bipolar disorder, there are some tests that can determine the diagnosis of a sleeping disorder and there is often a med free treatment. If there is no sleeping disorder (or if it is treated successfully but the symptoms remain) one can always pursue the bipolar diagnoses. A sleep specialist may be able to do both depending on his/her background.
As a person who has been diagnosed with sleep anpea and plms but not bipolar disorder (at least not at this point in my life) I can say with assurance that I have gotten very hyper in the past when I was tired. I had a tendency to go and go and go almost as if I am on autodrive..however, I generally didn't get much accomplished and I often resorted to compulsive behavior because, I believe, sleep deprivation deprived me of the necessary concentration to accomplish a variety of tasks. I have also observed hyperactivity in some children but it was only when they were overly tired.
There is no easy answer to these questions...your friend could have one condition, the other condition, or both.