You don't actually state your reasons for wanting your girlfriend you change her privacy settings. Regardless of this, she is being rather naive as there are many risks associated with making her posts public.
For example, identity theft, fraud, stalking and burglary. It may also hinder her employment prospects, both present and future. She may also have her photos stolen for catfishing purposes or worse still, have them edited and placed on adult websites.
Furthermore, there is nothing preventing someone else setting up a fake account in her name, by using all of her information. Friend requests are typically sent out those on her list. If the friend request is accepted, these people risk having their information stolen as well.
I would advise your girlfriend that not only is she endangering herself, but she is placing her friends at risk also.