She sounds like a Yorkie....
And YES - just like human kids, they DO regress...
Mine did around 9 months old, so back to the beginning with basic training we went. I use positive praise and a yummy treat reward (Peanut Butter Chips from the Baking isle). I limited their freedom again, meaning when I was home, I set up "stuff" to keep them in the same room as I was in, this way I could make sure no one was doing potty in the wrong places, etc....It took a couple of weeks of "re-training" but then they were on track again.
The had free run of the house when no one was home when they were about 1.5 y/o |