It’s important for her to see healthy marriages and happy couples and experience all the positive aspects of married life…Instead of explaining what marriage is show her a beautiful happy married couple!!
She might be hearing/or experienced the negatives and unhealthy marriages or even divorces that have influenced her outlook…
A typical 19-20 yr old is excited to date and get married..so you might want to find out what caused the “no I don’t want to get married outlook”. Good luck!!