How do you know when a horse needs shoes?

Meaning, a new horse. She had always been shod when she was being driven because she was driven on roads and whatnot. Then she was put in a pasture for almost 2 years so she was kept barefoot (hooves were still trimmed and maintained routinely, just no shoes). Now I have her as a riding horse and I was trying to decide if she needs to be shod? She is half draft and has pretty shallow hooves.