"My colleague is on vacation, and I'm writing a letter to her."
Translation:Ma collègue est en vacances et je lui écris une lettre.
I don't think my answer should have been accepted as I mixed up the genders? mon collègue est en vacances et je lui écris une lettre. Mon collègue indicates a male while the statement says her. Oh well, I'll take it and move on as many other "correct" responses were marked wrong.