Why do they give 'elle assistait à' as a hint and then mark you wrong for using it. And passing an exam isn't the same as attending one or participating in one - 'taking an exam' is the usual phrase in English.
No, in English "passed" would mean she succeeded.
In French if you say "elle assistait à", it means that she was a spectator, not taking part in the exam itself.
Beware with the hints, they are general and not specific.
If I haven't seen some of these expressions before, there is no other teaching in the course to help me, except the hints, so I can only guess and get it wrong a lot of the time, and I get fed up having to keep repeating lessons.