Have you had a preliminary visit with the orthodontist yet? They may not recommend traditional braces due to her periodontal problem. Sounds as though she would be a good candidate for invisalign though. Traditional braces make your teeth even harder to clean, but the invisalign is removeable, so she could brush and floss as she normally does. Without knowing if she has any bone loss (the usual reason for loose teeth), I couldn't guess as to whether she would lose any teeth. I hope not! 13 is really young to be experiencing this problem.