Hi Rakhee,
What have you done so far?, hows it going to date?
as a general approach I would work all of the systems, paying particular attention to digestive, lower thoracic and lumbar, groin, nervous system and use lots of relaxation techniques to reduce stress levels. As well as all this I would be looking to understand the root cause of the IBS( inc emotional links). Dependant on the Client I may also refer to a Kinesiology colleague to test for allergies/intolerances.
hope this helps!
Lisa x