Mara never appeared in the films, thus she is some lady. On the other hand, virtually no one has ever made any medium involving Superman without Lois.
She is the only character besides Superman/Clark Kent who had any lasting presence to appear in the first comic. Let's see what else we get. They have introduced her in JL8. I had friends who were confident in saying "Clark is going to marry Lois", in their assessment of why it was so stupid Clark was pining for Lana in Smallville, and that was at latest during Smallville Season 2. These guys knew where it was headed, even when her character had not appeared yet. OK, I mainly just wrote that because I wanted to point out that that is how major Lois's role is.
