Remember that Gerson's program is 75 years old, some of his principles must be revised based on the knowledge that we have today. For instance, he recomended raw beef liver juice, but because of the problems with today's beef, Charlotte Gerson has moved to dessicated liver.
His generation did not have the understanding of the mechanics of fats and oils that we possess today. We now know that certain fats are essential for good health. Cold pressed olive oil, flax oil, etc. should be OK. Remember that oils can go rancid rather quickly. I buy flax oil that has been cold pressed, and refrigerated. I buy cold-pressed olive oil, and use it quickly.
As far as cooking, you should try to avoid cooking with oils as much as possible, and then only a small amount.