How do you console an ugly girl who complains about being ugly?

Thankfully, I haven't had a whole lot of ugly girls ask me if I think they are ugly, but every now and then an ugly girl will share her frustrations with me over being unattractive. I don't know what to say. My knee jerk reaction is to say, Oh, you're not ugly! but that's dishonest, and I think most girls in these situations would know I was being disingenuous. But what am I supposed to say?