I agree, try a pee pad and there is even a spray you can spray on the pee pad that attracts the dog to pee on it.
Yes Yorkies are one of the harder breeds to house train. Some Yorkies even take up to a year to fully train. Just stick in there and be consistant with her and she'll eventually get it.
My 7 month old Yorkie (Bella) is still not 100% trained yet. She's fine during the day and at night I crate her (she has a pee pad in there) but in the morning I always fined pee in her bed and I don't understand why she won't use the pee pad at night
So I end up washing her bed every day
It is frustrating but she's worth it
Good Luck!