I tend to believe some of this story is true. It is unfortunate though that the source of this particular story is a right wing nut job rag, but I have heard some of this same stuff from a source or two that I find more credible.
I don't know what Mrs. Obama's interests were or undergraduate major was back then. I can tell you that while I was involved in a political science club at a mid sized, midwestern state college, we had a fair amount of interaction with a similar club at Princeton, along with many other schools, including others from the Ivy League. It was not uncommon, in fact it was commonplace, that the students we interacted with, almost 100% white, carried what we might now refer to as an outrageous sense of entitlement. They were quite taken with themselves. They spoke as if they knew they would one day run the entire country. They acted as though only what they had to say mattered, and they had no respect for those who were not of their "breeding" so to speak. There were no blacks at all in the groups I encountered in the Princeton University World Affairs Club.
I can only speculate what it might have been like for a black woman from inner city Chicago to thrive in this type of environment. I have to believe it was more than difficult. For a young woman trying to make a name for herself while knowing she was only there due to her brother's influences, she must have had quite a chip on her shoulder.
It's no secret this is a strong woman. It's hard to believe she was actually drawn to "Marxism" purely for it's principles. It's far more likely she was simply looking for a way to rebel against the white tyrants and this was as good a way as any.