How long are you staying outside when you take her out to pee? My old dog used to pee a little in one spot, then pee a little in another...it took such a long time for him to get it all out!
Do you pick her up and bring her outside when you catch her peeing? I feel like that's the best way to stop it mid pee and teach her to go outside. I did this with our other dog, and not once did he pee on me...so that's good
We taught our last dog to hit the door when he wanted to go out. So he would literally hit the door with his paw and we could hear tell us when he wanted to go out. That would be another idea if you don't want to do the bell. Have you tried praising her with treats when she pees outside? You may need to up the ante a little...while simultaneously helping to train her bladder to last a little longer!