"She goes up to the mountain."
Translation:그녀는 산에 올라가요.
Another example of the inconsistency of the course. Either 가 or 는 could be used depending on the situation. If DL can't provided the context to teach the different nuances, it is unfortunate. With no prior reference to the girl (or woman) and no special emphasis or distinction comparing her to someone else; if just happening to notice and comment on a women climbing, it seems appropriate to use 그녀가 .....
I am guessing it can. Because in another question, "The busy student goes up to his room" is translated to "바쁜 학생이 자기 방으로 올라가요." I was marked wrong when I used "에" there though. It could be quite confusing for learners when such inconsistencies exist and there is no explanation.