You are absolutely doing the right thing. It does seem to take yorkies longer to potty train than other dogs. Are you able to stay at home when them during the day? If not, what do you do with them while you're gone??
I don't think introducing the bells in too much. The only other thing I could recommend is if you see them going potty in the house, clap your hands real loud and give a stern NO. Then take them right outside and if they finish up out there, then give them a treat.
Welcome to YT! You will find a wealth of info here on this site. You could do a search for Potty Training and you will find lots of info that way, too.
GOOD LUCK! Don't give up. It seems like you are doing everything right at this point. I am sure that she will get than hang of it in no time at all.
