Hello there,,,most probably it is a hamstring tightness/strain
It needs proper evaluation ,,,,however if you give a detail history it could be a bit clear
1)like was the delivery normal or operative?
2)was this strain during the pregnancy also or started after the birth of baby?
3)what is the frequency of this cramps ur wife gets....like once a day,3ice a day ??
Next Steps
her food nutrition should be checked,and electrolyte contents(ORS) should be added to oral fluids which should be consumed in a large amount.
Health Tips
if its a simple muscle strain it should respond to muscle stretching,IFT & prescription muscle relaxants.
do get back for proper and detail analysis with her reports.
Regards & take care.