"Did you see Mara? Yes, we saw her."
Translation:mara bolegh'a'? HISlaH. wIlegh.
It is not necessary. If you were typing, the answer, mara bolegh'a'? HISlaH. wIlegh. would also be accepted. ghaH is a pronoun referring to a being capable of speech. Without context or the pronoun, wIlegh could be interpreted as "we see it." Using ghaH makes it clear that we mean, "we see him/her." However, the earlier question in this exercise makes it clear, so it doesn't even really provide clarity here. It is completely optional and the Duolingo software just seems to have randomly included it.
The pronouns and their uses are taught in the Tips & Notes of the very next skill (on this same level). Theoretically the software should not be showing you pronouns in the best translations until you have completed the Pronouns Skill, but it isn't always perfect about it. There is a way for us to make sure it doesn't show up like this, so I'm going to go make that change.