After being cut open through the lower abdomen - whether it is to insert a new kidney (yes! a kidney transplant is housed in the pelvis!) or a more common c-section... the lower abdominals will be cut through. This will mean that no matter how long you wait those muscles will not 'come back to life' naturally. You will need to work on them. 

Initially you will need to convince the muscles to switch back on. The body has a frustrating habit / mechanism of switching off stability muscles specifically when there is pain involved. This may be the spinal muscles after a bout of back pain or abdominal muscles after surgery. 

At the beginning it is important to assume a rested posture on your back with your knees bent up. You must purely focus on tightening the pelvic floor. If you put your fingers just in and inch and down an inch from your boney bits on the front of the pelvis you will hopefully feel a tightening there. You will therefore feel the effect of tightening the pelvic floor on the deep abdominals, i.e they are linked by the same command. This process can be watched on my 'Introduction to the basics of mat pilates' video on YouTube.

You can then work though the 'Basic Pilates Workout' for around 6 weeks. 

After this you may feel much better but if you still feel tightnesses and vulnerability you must work into different planes more confidently. You will therefore benefit from a few more complex movement exercises. In which case check out the combination of exercises below.  

If the scar is giving you trouble it is beneficial to do some scar massage - without any cream place a finger not he scar, keep it in contact with the skin and use circular motions taking the top layer of skin with you, use moderate pressure. Work your way along the scar. This will make it less sensitive and more mobile. You can also use scar patches. Check on Amazon for Elastoplast scar reduction patches. They will be sent from France. These will help the scar to recover well too.