I was reading your blog and the trouble you're having with Annie. You are not alone. It's not only chihuahuas that are hard to potty train, it's mostly all small dogs. I have a very small female min pin who was originally pad trained and it took me forever to get her off the pad, but I still have issues in the house. I had to put her back on the pads because of this knee problem and she's not suppose to be out. If you want to train Annie to go on a pad there is a spray you can get at the pet store that has the pheromons from dog urine. Spray that on the pad and that should teach her to on the pad instead of your carpet. I had to use it outside with my male min pin when I got the yard fenced because he refused to go in the fenced yard. It's taken two years, but he's finally doing everything in the yard.
Plus, little girl dogs are harder to potty train than males are I think. I've never had an issue with training a male dog, but this little female is really trying my patience on the potty training.
I hope this helps. If she does have a specific place in the formal room, put a pad down in that spot and hopefully she'll use it. That's about the only thing I can suggest right now.
Also, with very small dogs like Annie you don't want them outside by themselves anyway because they're perfect bait for owls, eagles and any other large predatory bird. My two are never outside without me out there with them.
Talk to you later.