The conjunction "а" has both a contrastive meaning and a contradictive meaning. In its contrastive function, it is used to join two or more complete statements that are placed close together for contrasting effect. In this usage it is usually translated as "and", with the connotation "while, whereas".
I am sick of Anna and Она being literally indistinguishable in these lessons. I had these problems in the beginning and I am still having them many lessons later. I am convinced that every non-native speaker has this problem. Reported it. Something needs to be done about this.