I'd be very concerned. Make sure she gets in contact with her doctor. You said that she is already feeling "happy". 1 week is a ridiculously short period of time for someone with major depression to respond to an antidepressant. Obviously I can't diagnose, but it is highly likely that your friend is actually bipolar, and the anti-d is sending her into a mixed or manic episode.

She needs to see her doc, pronto. This is an emergency situation.

You're a good friend for caring so much about her. As someone with a mood disorder, I can say that we appreciate kind friends immensely. They can't cure us, but they can make life with a mental illness much more bearable.