My sister is working with an MNC in Management Information Systems process responsible for budgeting of projects and cost controlling etc, also indulged in procurement of parts in oil and gas division of the company. How is Six Sigma beneficial for her?

If your role is limited to creating MIS reports, you may not have much opportunity. But as your message suggests, you are responsible for cost controlling, procurement of parts etc.

This means you are involved in processes that can provide better results if you carry out improvement projects using uncommon but tried and tested management techniques.

Please note that for a problem, if the solution is already known, it is not considered a worthwhile Six Sigma project. For complex situations like yours that require cost reduction or control, Six Sigma techniques are extremely useful.