retrolisthesis with chonic disc prolapse

hello friends i m dealing with a 38 old female,who came to me six months back with symtom of neurological cludication without back pain.she was having reapeted attack of back pain previuous.treatment given in form of flexion exs,deap heat, streachings and TENS.she was completely ok in 1 week.after 6 months she again come with sever back pain,unable to do slr in both legs in lying but can flex spine in standing with lumbar lordosis.extension was painful at end range.case was refered to ortho,who give her muscle relaxxant and pain killers for 10 days and rest.she was ok from next day but advised for m.r.i.m.r.i shows grade-1 retrolisthesis of l5 over s1 withposterior and left paracentral disc herniation of the l50s1 disc compressing exiting nerve root.
right now she is having pain in standing and walking.also in sitting for half and hour.all these symtom developed after hearing m.r.i report!ortho ask me to start physiotherapy and mild extension exs.i argue with rest for few days than for flexion exs.i dought regarding stability.how can we jugje wather it's a stable listhesis ot r not?from when i start physio treatment?which type of exs?as one of my friend dashrath also had retro listhesis.posted his form here 2 years back,but i can't find it here.
with regards,