consult an ortho.
take out Xray lumbar spine
u might hv to go in for a MRI if problem is severe.
it can be that she is suffering from prolapse intervertebral disc
does she hv associated tingling
and numbness in her legs?
bed rest is imp initially for her.
consult a physio after investigations.
they will show u various exercises available.
ask her to avoid bending with back rounded.
practice lying on stomach for 5 min thrice a day.
hot water foment the back twice a day.
apply local analgesic
to ease the pain