Can The Width Of Her Mouth Could Be Narrowed With Braces?

I am a SLP working with a 9 year old with a lateral lisp. Her hard and soft palate look normal (slightly high arch and wide not narrow dentition). Air escapes unilaterally and she claims that she can't stretch her tongue to both sides of her mouth to seal off air for production of sibilant speech sounds. She also has enormous tonsils which the physician states will disappear by age 16 so removal is not recommended. Do you think it is possible that the width of her mouth could be narrowed with braces so that her tongue would extend on both sides to her teeth and the lateral escape of air would be eliminated?