That's a pretty mild diagnosis, but she might get glasses to use just for certain activities (like reading a chalkboard from across the room). The way it breaks down, 20-20 vision means that if you have a theoretical person standing 20 feet away from a sign and they're able to read it perfectly, so can the real person taking the vision test. So with 20-50 vision, your daughter would need to stand 20 feet from a sign to clearly see something that a person with perfect vision could see clearly from 50 feet away.
In comparison, my vision tends to be around 20-1600. So what someone could theoretically see perfectly from 1600 feet away, I would have to be 20 feet away to see. That makes me legally blind without corrective lenses and I'm not allowed to drive without my glasses or contact lenses. I can see clearly up to about an inch in front of my face. 20-50 really isn't anything to worry about.