Get her vitamin D3 levels to near or just over the upper end of the range…D3 deficiency mimics MS and is pandemic in the northern hemispheres this time of year especially. Easy and safe check is give her a half million IU of D3 (not enough to come close to toxicity, but enough to very quickly unmask a deficiency) and if she starts feeling better within hours and improves over the following days/weeks, you have your answer. This is an epidemic.
https://vitamindwiki.com/Multiple+Sclerosis
The site is run by an older fellow and it looks like his cert is expired…the site is cool though and a deep dive and labor of love… be well and peace to you and your little sister.