My misses uses a 3x4ft pole all the time no problems, sometimes she uses a 4x5ft pole but it is bit of a struggle for her and only on fairly simple windows no over the conservatory jobs.
Your asking the wrong people really as we don't know what your wife can lift. Tread carefully though as you might be cooking your own dinners for a while if you do the wrong thing.
I think the wives that go to work with us are a great thing, I wouldn't be without mine.
Simon.