What test does my mom need? Please help be a detective for me:

My mom is 80 but was always very active. Right after her mastectomy, she spent whole days laying in a soft chair and sleeping on her left side. After 11 days of rest, she walked a few blocks to the movies and on the way, her left leg felt a little sore. When she rose from the movie theater seat for 2 hours she had severe sciatic-type pain in her left leg.

2 days later, the pain was so severe, her GP told her to go to the ER to check for a compression fracture. (She has severe osteoporosis and is 80 years old)

They did x-rays and found.. NOTHING.

We just saw a physiatrist and he said her symptoms match with Neuroforaminal Stenosis and that the L5 root is being affected. (i suspected a herniated disc, but her symptoms are the opposite). She can sit in a hard chair indefinitely with ZERO pain, she can bend forward painlessly.

Her pain is worst at night, lying down. Some days she can be pain free for a few hours, but it acts up at night.

This last part sounds like bone metastasis, but her oncologist said its unlikely because she is node negative with no LVI.

The physiatrist said he will order an MRI on Monday if the Gabapentin isnt helping enough. He also couldnt explain why the stenosis symptoms came on so suddenly.

If he orders an MRI, should I ask for it to be "with contrast"? Is that how tumors in the sacrum or lumbar spine are identified? I dont want her to get one with contrast when she may also need some other test that uses a radioactive infusion (like a bone scan, i think). SHe already had a breast MRI with contrast last month, right before her mastectomy.

Any advice on whether an MRI with or without contrast is more advisable in this scenario? Or whether this sounds like metastasis? Or whether stenosis symptoms can occur suddenly?

Thanks all.