Differently able people (disability)

I recently went to shop at pnp Jubilee mall and I was certainly not happy with how the front end cashier manager was treating a deaf cashier. Having known that she(manager) knows that someone working under her (cashier) is differently able than other cashier should have been a wake up call to her to upskill herself as to how she can help her do her job effectively. The cashier wanted to void some stuff and obviously she can't call her but demonstrated to her that she needed help. The manager decided to ignore her and do help people who didn't even need help. That made me question her work ethic and pnp laws about how they treat differently able people. I mean if they can't work a way of how to treat and help their employees, how would they care for the customers that come in day in day out which are differently able?