Awww she is a cutie patootie!!!

her sweet little face!
What helped me when my pups were young was to set a timer, I did this on my cell phone. It would go off every 2 hours and I would take them out. Then I would increase it after a week or two to 2.5 hours, then 3, then 3.5, then 4, then 4.5, then 5, ect.
Them understanding NOT to do it in the house is usually a problem. They want to pee in the house, to mark it as territory and very natural/instinctive. Keep reinforcing anger at the mess itself is working for me with my Yuna, who was trained but then decided to not be. LOL
I freeeeeeeaaak out at the mess in the house. (overly dramatic, disgust, omg, this is awful, so horrible, how could this happen? Disgusting! Oh no! Why? Do some fake crys like it is a tragedy)
But I never direct it at Yuna. Since I have been doing this there is less accidents, and where there is it is because she very much had to go potty...
As far as the age is concerned, some get it very early, even as early as 8 weeks, and some don't get it until later. Just depends on the dedication of the owner with the training.
Best of luck, cannot wait for more pics of your baby!
Afterthought: Perhaps carry her down the stairs until she is better at holding it?