You might want to choreograph the scene first and then add the lines. Stage it and have them say anything they want just for the moment.
The scene is a lulu, but is not the whole play.
It will be harder to isolate Helen emotionally by lack of sight, sound and speech than it will be to stage a giant contest of wills. The hitting is incidental. It is one of Helen's ways of communicating.
Get your Annie Sullivan to learn an ASL alphabet. There's lots of method homework here. The play is deceptively difficult from a technical point of view.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher