"My friend is a student."
Translation:Моя подруга - студентка.
Nothing. The authors of the course decided to just give you male and female sentences interchangeably, with both translations accepted. This way you get exposed to both "студент" and "студентка", "друг" and "подруга","письменник" and "письменниця" and so on, however, you are never forced to use the female option.
The alternative would be to use the awkward "My female friend is a female colledge student", "My mom is a female teacher", "She is a female writer". This would only feel natural for "waitress" and "actress", which are still acceptable in English (even if discouraged as sexist in some formal settings).
When there is nothing to suggest that you are talking about female, both should be accepted.