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.