Hello @kandc317, I apologize for the delay in response.
I'd like to invite @lisal64, @blessing19, and @larsmayo who have all talked about mobility issues in themselves or someone they are caring for. Although the causes and location of the mobility issues from multiple myeloma may be slightly different than your wife's, they may have some similar experiences and concerns as you.
@kandc317, did you and your wife discuss the potential for decreasing or altering the chemo treatments so that she could gain strength in her legs back? Did they think this was a plausible compromise, were the treatments set to be the same regimen for the foreseeable future or are her current treatments to get the myeloma under control in the short-term?