What do you think of the name Riley Erin/Aaron for a girl?

A friend of mine is thinking of this name. Her husband's name is Aaron, and he is overseas and will not be home in time for the birth, so she wanted to surprise him. They thought they were having a boy when he left. And they wanted Riley Aaron. Should she go ahead with using Aaron or go more feminine with Erin? She said she likes it like Aaron and it is not as if they will be using a hyphen or anything. She is due in two weeks, and is SO afraid she is going to choose the "wrong name."