I HAVE A SIX MONTH COCKER SPANIEL/POODLE CROSS WHO WAS IS ALMOST 100% TRAINED BUT IS MANIFESTING SIGNS OF REGRESSING.This morning was the last straw when I put her out to pee,she didn't,so after 10 minutes brought her in and left the door open.She immediately ran upstairs and peed on my unmade bed.
I put her outside immediately and she is still there,30MINS later, at the window,probably wondering what she did wrong!
Should I go COLD TURKEY and leave her there all day!

NO... she doesn't any idea what she done wrong. You will most likely have to take her outside. Does she go to the door when she has to pee or show you some sign? The last puppy I raised done the same thing... it was like he forgotten everything he knew about going outside... I just kept urging him to go outside . I only scolded him for peeing in the house and he hated that... soon he was going outside again.

Do you give her treats when she goes potty outside? If you do, do you give them to her while she's still outside or after you bring her in?