Just this past Monday I also bought a yorkie on craigslist named Bella
She is also 4 years old and 100% potty trained to go outside. I also wanted to train her to use the pads. I left them down for 4 days constantly telling her to go pee pee on them but she just wouldn't, she thought they were little blankets for her to lay on
She can hold it for hours, then eventually she just cries for me to take her out. I just gave up and decided to keep taking her outside to potty. I'm just thankful that she doesn't go on the carpets lol. When the evil New England winter hits it's not going to be fun but when I take her out if shes just sniffing around being nosey I tell her to go pee pee and she does. I'm moving soon and in the new place I will be able to stand inside and let her out on the long leash to do her business lol. I don't think she will mind because she probably won't be enjoying the cold either