Is her engine a direct injection engine? If so, not surprised. Has nothing to do with the gas.
Just looked it up. Yup not the gas fault. This is a known problem with direct injection engines. VW has some literature on this and people over at vwvortex has documented this through and through. This is a very common problem. In fact, her car is one of the worst and most known.
http://www.autoguide.com/auto-news/2...-engines-.html
Do a Google search, it's all over the web.