Fredagen translates as the Friday so I was marked as wrong. Why not write "Hun arbejdede ikke om fredag".
That would not be right. It should be the Friday as you write (one incident) or på fredage (if general).
This exercise should be reviewed.
I was about to ask as well.
I'd also like to know this
Native english speaker here...It's a tricky sentence. I would say "She doesn't work on fridays" or "She's never worked Fridays".