My sister who is 13yrs old has genu valgum. she has a 6~7cm gap between her feet. what can she do to make it normal again? what type of treatment?

At that age...: At 13, there is quite a bit of laxity in the joints and ligaments due to puberty. Is she having pain or is she having problems walking - those are questions you want to know. See a pediatric orthopedist to determine if the genu valgum is structural or functional. There is a difference. Surgery should be considered last, but p.T., bracing, stretching may be options.