Dear Stressed,
The possibility that she is a P is certainly there but it is too early to tell. Kids who are angry, hurt, or feel rejected also act out in very cruel ways. You might also want to read Internet info on attachment disorder (also known as Radical Attachment Disorder). The symptoms are very similar. At this point, I would recommend that you get her into a therapist that specializes in RAD. If this is what she has, therapy can help to minimize behaviors. If not, you'll know that you are doing your best to get her some help.
There is also some excellent advice about dealing with P's on this web under coping with the adolescent psychopath. These tips also work well for dealing with those with RAD.
I would recommend joining a support group (do it even if your husband won't). There are many groups for RAD parents (most are adoptive parents but they experience the same behaviors and pain). Tough Love International (now called stand up parenting) primarily focuses on adolescents and older but if you have a strong group they can help you detach and not get sucked up in the vortex (I speak from personal experience).
Don't let her destroy your relationship with your husband and try to avoid becoming the heavy. My 27 year marraige almost hit the rocks because my child's manipulation. Hubby couldn't believe child could be so cunning and conniving.
Finally, create a paper trail by dating and documenting behaviors. It will be a great help to anyone treating her and also to recognize patterns of behavior. I e-mailed my child's therapist with an update the day before our sessions. Then we didn't waste precious time (and money) on recaps and could get right down to what we needed to do.
Hope this helps...Hang in there