See if a hot bath and nurofen helps. If it does, ride it out.
If it continues to get worse, or
she feels like she is getting pins and needles or numbness in any arms or legs
One side of her body gets weak
She starts to run a temperature
Her face starts to seem lopsided
Or her speech goes odd
Then call for medical advice
If she is still needing significant pain killers in the morning, take her to the doctors as she might be better off with a muscle relaxant rather than lots of neurofen
She has probably just put a back muscle into spasm and that one is now starting to yank on all its neighbours and set them off too.
Actually if she can sleep on her back try and prop her with pillows to keep her neck/head well supported and both arms on each side, sort of like a cocoon, even get her legs supported under the knees, if her limbs and neck arent relying on her back muscles to support them, her back muscles might relax iyswim