Your mother has two different conditions in the lumbar spine. One is spinal stenosis and the other is a disc herniation at L5-S1. Unfortunately, the physical adaptation for stenosis competes with the compensation position for the disc hernation.
Stenosis is the narrowing of the lumbar spinal canal. Standing reduces the canal diameter even more and most patients tend to lead forward when they stand and walk. Stenosis is posturally compensated by what is called posterior pelvic rotation. Rotating the pelvis backwards (by contracting the abdominal muscles and buttocks muscles) opens the canal but allows the patient to stand more upright.
Disc herniations at L5-S1 typically compress the nerve roots with sitting and most patients compensate by standing to reduce the nerve compression,
Your mother may have both problems which puts her between a rock and a hard place (a dilemma). Compensation for stenosis (leaning forward and sitting) is the exact opposite of compensation for disc herniation (standing). The only position that accommodates both is lying down.
Your mother can travel but travel might be uncomfortable for her. I cannot comment on the need for surgery as that requires a workup to determine what surgery would be helpful.
Sleeping should be most comfortable either with a thick pillow under the legs when lying on her back (90/90 position) or curled up with a pillow between the knees while lying on her side.