Macha is a human living in Kirkwall, and the sister of Keran.
Background
Varric's sources say that a woman by the name of Macha has been desperately seeking a particular templar. She's been spotted outside of the Chantry in Hightown during the day.
Involvement
Macha is involved in the quest Enemies Among Us.
She is very worried about her templar brother, Keran, because he used to write to her every day when suddenly the letters stopped arriving. She asks Hawke to speak with the templar recruits in the Gallows to find out what happened to him.
After Hawke rescues Keran, Macha will be with him at the Gallows as Cullen is assessing whether or not he should remain in the order. Hawke can either convince the Knight-Captain to allow Keran to continue his training, or be expelled from the order. Either way Macha will send Hawke a letter expressing her thanks.
If Keran stays with the templars Macha will express concern over what the templars will do to him but recognizes that staying is his choice.
If Keran was expelled from the Templar Order, Macha will fall into debt with a Tevinter loan shark named Senestra. Hawke will be asked to deal with Senestra to help the siblings again.
Result
Macha fears she will be unable to pay Hawke, however, they receive gold from Knight-Captain Cullen.