Oh mostlylurking, i sympathise with you completely. My DD is 14, nearly 15 and just going through the normal teenage angst and hormonal changes is bad enough without the added turmoil your daughter is in.
Why does your daughter think she is bipolar?
Could she just be very confused with all of the changes her body is going through cos i know how much my own daughter is struggling with it all.
I agree that maybe a talk with her form teacher might be a good idea, see if there is anything that they have picked up on.
As for the being a single working broke mum i can fully understand how you feel, its a constant struggle just to keep everything going day to day. I am also a carer for my disabled parents so i know how hard life can be with no support. Cant really offer advice on this but can honestly say i do know how you feel.