Ok any adivce would be great!

My little girl is almost 8 months and she's still having accidents. I'm working really hard to keep her on a schedule and let her out every three hours, but she still has poop accidents in the house. She doesn't pee inside anymore (for the most part) but poop accidents are pretty common as she sneaks away to do it.
I praise her with treats when she goes outside, but she never tells me when she has to poop. Is this normal? What ages were your pups when they finally got it right? thank you!