If that doesn't work (though it should help) then what you have to do is when she potties in the right spot, and she goes (or squat like they have to go) LOTS OF PRAISE and positive attention!! When she goes somewhere else don't give her any attention at all for it. If you catch her in the ACT of peeing where she's not supposed to, tell her "NO!" then pick her up and place her on the pad and if she goes, even a little bit, PRAISE!!!!

It's a tedious process and a very frustrating one too!

If she's 16 weeks though, can't you start training her to go outside??