Personally, I would say yes she should. A marriage proposal should go hand in hand with presenting a ring to seal it. although nowadays, even if the man's proposing, it normal ends up with the couple going out together another time to chose the ring together. I think this takes the romance out of it as the man you're marrying should have an idea of what ring you would like. So I would say that it would be best to do it with a ring, and it doesn't have to be expensive. Good luck to them - all the best for their future.