re-engineering brakeing

i have a 10 year young daughter thats been riding for about two years on mostly flat land.she does incredably well for a child that has cerabal palsy.to discribe how she is aflicted,she is a 65pound baby thats not very stable walking yet and  comunicating or understanding is that of a 2-3year child.anyway braking is the issue if she wants to stop she will coast to a stop or intensionaly run into something or some-one.she does have great thumb-throttle skill,but because of her lack of stringth & reach and in-ability to operate the hydraulic brake lever,i want to change it to a push button brake that has to be held to ride and locks when the button is released  

they do make braking systems like you are speaking of, they are electronic and used in some forklifts.

check with yalecarolinas.com see if they can help you out.  
Keep it RUBBER SIDE DOWN!!