Tricks to getting patients to do what you want?

Umm... It sounds like not taking a bath was her technique for controlling something in her otherwise chaotic life. You said that she was Hindi; does she have any kids? Sometimes the more 'western' children of immigrants hold sway over getting the parents to participate in their care.

To reiterate what others have said, you give the choice of when or how they want the bath, not if.

However, to be culturally sensitive, many other cultures aren't as obsessed with bathing as we are. Educate on the infection risks and address those issues.