Maybe I am mis-reading but what I am getting from your post is you would like her to eventually go outside right? You have her on piddle pads now and are trying to also get her to use litter? That is all very confusing to a little one. I personally feel the first thing a breeder should tell a potential buyer is yorkies are a bit stubborn and take a while to potty train. I train mine probably different than the next and they do different than the next and so on. I can only give you my method and you do as you wish with my personal process.
I put a piddle pad by my backdoor (leads to my fenced backyard). I use the SAME command each time "Who wants to go outside"? Then I open the backdoor and eventually they learn to go out. Most dogs that live inside have a sense that grass=pee. You will need to use the same command over and over consistantly through out the day. Praise is a must to allow her to know she did something right. The piddle pad I use if they need to go during the night or when it rains or snows here. If you do not have a fenced yard, continue to use the piddle pads until she has received all her shots. I would suggest keeping the pad out of human sight and in the same location for ease in the future i.e. backdoor, laundry room, etc. Then after the shots, let her out in a fenced yard or with a leash on a walk. Piddle pads are a GREAT tool for cold areas as you mentioned. Just don't confuse her in your urgency to get this taken care of quickly and introducing her to 3 potty areas is confusing. Best rule of thumb is, they have tiny bladders and like babies, they do not understand there is a designated area. It takes LOTS of time and patience that is true. I have yorkie mommy friends that still have potty issues at a year old. I thankfully feel my method has worked personally. If you are not consistant and stick with one location, you will fail. I hope I helped
Good luck!