Is she having this problem after delivery.If so its quite common because around 10 to 12 kgs of weight (baby placenta fluids) was partly supported by the back muscles during pregnancy.
And due to hormones in pregnancy makes all this mucsles to relax during that times .
So it takes around 4 to 8 weeks for these muscles to return to normal shape.
I suggest her to avoid bending and lifting weight including baby for some time.she can bend her knees and take the baby or weight.
You can consult an orthopedician if problems persist .