lol i think Yorkies just cower... honestly- Layla is loved more than any dog i know- yet she still cowers. we always say- if we died today and someone else had to take Layla- they'd say she was abused.... we can't figure it out.
Try doing sit with her back against the wall so the will back away from you and be forced to sit down when she hits the wall... then use your hand to gently put her bum down so she knows where it should go
Hang in there! She'll get it!