Oh Catt thats wonderful
See Jane you got friends there already and you don't know it!
You're a midwife *hats off to you* it's a very very wonderful thing you're doing!
Slicker brushes work well BUT not for a first grooming to get tangles out, they will hurt and pull. Start in a small section and use a paddle brush, they almost look like our human hair brushes but they are wire bristles tipped off with plastic so as not to hurt.
From the mix, it sounds like you have a big fur coat there (giggles) and it will take some time getting used to grooming.
Nipping can be very typical of border collies. Have you noticed that she doesn't like to have you stare into her eyes and is she nipping at heels mostly?