Don't give up on that little girl, there's always hope.
You said she can't hold it longer than 6 hrs during the night...Try buying some puppy pads for her to use at night. We live in a 3rd floor apartment, so we can't take our yorkie up and down the stairs all the time (especially at night) , so we trained him to potty on the pee pads. He goes #1 and #2 on them.
Are there certain places in the house where she likes to pee almost everytime? If so, try putting a potty pad down there. That way, when she pees there, you can positively reinforce it by giving her praise and maybe a treat.
I know it sounds tedious, but when you're first trying to potty train a dog you have to be very persistent and very conscientious about where the dog is at all times so that if she has an accident, you can immediately (if you wait a minute or more, she won't know what you're doing) take her where you want her to do her business, whether it be outside or on a pee pad.
Don't rub her nose in her business or anything like that...DO give a treat or give praise when she goes potty in the right place. It takes time for them to learn, but they will learn.
Everytime our yorkie does his business on his pad, we throw a big party for him and he gets all excited. He loves it, and he knows that good things happen if he goes on the pee pad. This helped ALOT when training him.
Hope this helps!
Yorkieluv
P.S. sorry for the long post