My 3 year old GSD wont eat?

We bought a German Shepherd ***** about 6-7 weeks ago. The previous owner used to leave her food down all day and we realised this was why she was so underweight. We took her to Pets at Home and they put her on Wainwrights which is just brown kibble biscuits. At first she loved it but then after a few weeks hardly touched it. She'd spit it out and leave it. As a result and us not wanting her to lose the weight she's put on we tried mixing fresh tripe with it. Again, she loved it and cleared her bowl several times. However after a bit god bored of the tripe and wouldnt touch it. We then tried wet food mixed and as before, she loved it. We carried this on several times but then reealised she would only eat the wet food. Now she wont touch her food bowl unless there is a full pouch or full can of wet food in there. She will eat the odd biscuit. Yesterday we bought her a different make of food (Bakers Complete as it looks way more appetising) and she loved the first bowl we gave her. She couldn't get enough of it. But this morning i've found when i gave it her at her routine time (1pm) She wouldnt touch it and went to sleep instead. So again, i mixed half a pouch of wet food in and she ate a few biscuits and walked away. So i decided to put the full pouch of food in. She's eaten half of it and left it, so i've now put it away in the cupboard as she's had too long to eat it and if she doesn't eat her dinner within half an hour to an hour we take it away as we are trying to get her into a routine! please help!!!!!!