You really do have to go outside with her to watch and make sure you SEE her peeing/pooping. When she goes, PRAISE and treat! She has NO idea that she's doing something good/bad when she potties. If you're outside with her for 10 minutes and still no potty... bring her inside and put her in a crate where she can't pee. I got Jackson as a young pup in December and it was freezing... so if he decided not to pee, he'd go inside and right back in his crate so I know he wouldn't go on the floor. He'd usually whine 10 minutes later... so we try it again and he'd go. Then he got his play-time outside of the crate. Eventually, he associated going potty outside with coming inside for playtime. It's a lot of hard work when they're puppies but it gets better!
It's a matter of being diligent, having lots of patience and getting them on a schedule. That first month, I tried to not even ALLOW an accident... I did this by watching him like a hawk when he was not crated or in his ex-pen. When I couldn't keep my total attention on him... in the crate or pen he went. Don't give freedom because they will put their smells all over your house and never stop going.