It looks as though descriptor 6f is the one you need. You could get 8 points with this one. You need to explain why she can't manage, though, and describe the help she needs.
I never have believed that 'just' ticking a box is enough!
Just been rereading the PIP guide - if you mean your wife can't manage at all to dress herself, then 6F applies. If you mean she can manage with help, then try 6d and 6e. Doesn't make eight points, but she should get some.
