While I don't think native English speakers should have to prove they can speak English, I do see the point of the rule. In order to gain US citizenship, one must prove that they can understand basic English, as the naturalisation interview is done in English only....so things are pretty much the same over there. Being able to speak the language is essential if one is to assimilate (and I don't mean completely, so don't pick me apart on that!) and interact with society at large.
I guess I'd ask why the woman can't prove her ability to speak English. Can she not produce a certificate from an English-speaking school? If she can speak English, she should be able to do what the rest of us will have to do when we apply for citizenship--produce a diploma/degree from an English-speaking institution, take an ESL class, or be certified by a qualified teacher. It's a dumb thing to have to do, but if that's what they want, then we have to do it.