I got pretty f’d up in the woods about 10 years ago. IMO dirt is pretty unsafe, too. You can’t really say it is safer than street. I would agree that both can be dangerous, but there are many things in life that have a level of risk. The safety courses are great to teach you how to avoid bad situations. The other thing is to not get cocky. Anyone can learn, no matter how many miles/ridning time they have under their belt.
Invite her to take the course with you. She will have a much better understanding, and possibly change her mind.