Lois is really intelligent, particuarly in seasons 5-7. They begin to show a lot of parallels between Malcolm and Lois. It also becomes evident where Malcolm gets most of his intelligence from. The reason she works at lucky aide is because of 'the boys', it's implied through most of the series, sort of starting at flashback.
I think, majored English Literature- she seems that sort of person fascinated by verse and prose. And minored in French (in the ep. where Reese finds Lois's diary, she mentions the fact she wants to move to France)