Hello from across the pond and welcome to KH.
Yeah, it kinda sounds like you might have overdone it. Can you tell that the pain has subsided any since you've stopped knitting for a while?
Often soreness will go away after a few days; however, if the pain hasn't lessened any, you might want to high thee to a doctor to make sure there's nothing wrong there!
When I push myself too hard either typing or knitting and/or crocheting (or any combination of those), my wrists and hands get really sore. I often hold them under a pulsing blast of water in the shower, moving it up and down my wrists and on the palms of my hands. That helps a lot, as does massage--especially if you can get someone else to do the massaging. Other than that, it requires taking a long break to let it heal and then not going at the knitting/typing/crocheting quite so hard--especially without lots of breaks in between sessions.
It's sure frustrating, I know. Perhaps you can give your friend the blanket still on the needles (so she can see it) and then finish it at a more leisurely pace.