K-Y and Surgilube are about the purest and plainest that you can find. If those irritate her, there is no "less irritating" backup. She may want to try some vegetable oils. Safflower seed oil is one very popular massage oil that has no irritation for most women.

I prefer silicone based lubricant to water-based ones like KY because the water-based ones can get kind of "sticky" or "tacky" feeling, which can be irritating to me. Also, they last longer without the need for reapplication, which leads to less irritation. I'm a personal fan of Wet Platinum. But other good ones include Eros and Sliquid Silver.

Other benefits of silicone lubricant are that you can use it in water and because it does not absorb in the skin, it is considered hypoallergenic and people may be less likely to react to using it.