First step is for your client to get clearance from her physician to ascertain if there are any contraindicated exercises and/or movements. Following clearance I would have her pursue a general fitness program–cardiovascular, strength, flexibility–with exercises and activities that don’t aggravate the numbness or tingling.
I assume that you have doctor’s clearance and have spoken with the physical therapist for advice. If the numbness and tingling do not go away, she needs to be seen by her doctor again.
As a MELT instructor, I would show her some of those techniques while always being in communication with her about the presence of those symptoms. You obviously want to find movement that does not generate that. You can find those techniques in the MELT Method book which is widely available.
Other than that, I would build on the PT exercises, teach her the maneuver to engage abs in neutral, add a lot of Swiss ball,and take it slowly from there. Since she just did P90X, she was probably quite fit, and it may be difficult for her to go back to entry level. But avoiding those symptoms is initially the major task whatever she does. If it is a possibility, some aquatic exercises may also be helpful such as deep water movement with a floatation belt.
It’s a tricky situation in that sciatica tends to “move around” thus it can sometimes become frustrating as a trainer to implement a workout plan around the nerve pain
I tend to send my clients to a PT after a complete assessment by a qualified physician.
There are many things that can be done to alleviate the pain yet they can also make the pain worse thus I tend to follow the prescription given by a Physical Therapist.
Also, sometimes people think they know how they got it, but upon prodding questions it sometimes has nothing to do with exercising too hard!
If adequate rest, ice, and anti-inflammatory’s do not work, I’ve had great success with clients by having them foam roll the area prior to training and incorporate dynamic stretches that open the hips. We avoid running and and jumps anything that may cause impact on the hip/SI area. I always finish with static stretches for the SI but be careful not to over stretch the area and lastly stretch using runners lunge because often times the SI can tighten as a result of the iliopsoas muscle being tight.