It IS tough and frustrating - my oldest dog didn't learn till she was a year and it looks like the young one won't either...patience is all that works.
I think now that she is at 7 months I can see real improvement, but that's because I walk her at moment we get out of bed as the first thing, every time she has eaten, slept or played and I walk her for 30 minutes every time.
And like you give treats when she peeps and poops outside
Hope you can use some of this - good luck