"Pene" means also beautiful and should be accepted answer, as well as "fine".
'pen' is closer to 'pretty'.
I disagree here. Would you say rather "pen jente" or "fin jente" about beautiful girl?
I'd say "nydelig jente".
While the adjectives do have some shared meaning, to be consistent the course teaches 'beautiful'<->'vakker' and 'pen'<->'pretty'.
What are the rules about when to use -ene and when to use -a endings? I am trying to work out why 'rommene' is correct but 'romma' is incorrect, but you can use 'barna' or 'barnene', for example (and 'barna' is used much more often on this course).
romma should be correct, report it as an error