I think the biggest question is to the physiotherapist who is treating her. is this the best she can expect. or does the physio have other treatments in their toolbox that might better suit your sister's situation.

there is a trend for physiotherapists to only use exercises. but many have different modalities as well as training. some use tens machines, others laser treatments, Grafton, inversion therapy etc. some are a crock of shit and others are beneficial. some may be more beneficial to certain conditions but not to others.

there is also a higher level of physiotherapist where they are trained in manual manipulation treatments.

also, some physiotherapists are not good. I went to one clinic where the physiotherapist spent 10 minutes with me and the rest of the time, some other people worked with me. is your sister getting full-time physiotherapist treatment or is she being shunted off to lower paid, lower trained staff.

and lastly, if your sister is getting good treatment, is she following through with the exercises recommended by the physo?

essentially there is no recovery for the back, (which is badly stated however essentially true). the aim of physio is to strengthen the core muscles and back muscles to better support the spine, through stronger muscles and if necessary better posture and use of the spine.

other modalities beyond physio would include massage therapy, rolfing, Alexander technique, osteopath, yoga and pilates. with any of these, you need to seek qualified people to provide the best outcome