Is youre daughter unhappy?
If not, I'd be inclined to let her live her life in her own way.
Some people are just destined to live quiet lives, and are perfectly happy that way.
If you are sure that it is your daughter who needs confidence, and not just you who is worrying about her, then suggest she joins a loval night class, or hobby group, if there is something suitable.
I certainly wouldn't push it. I have three girls, and their temprements are all very different - that's what children do, be different.
Don;t worry, she sill be fine.