Picky Dog won't eat! HELP!

So here is a back ground on it. I have a english setter that i adopted from the animal shelter a couple months ago, and she weights 35 lbs. I would like her to be atleast 45 lbs.
But she is extremely picky. I had her on taste of the wild but she had the runs on that. So i swithed here to EVO red meat, and she really loved it at first, then i started putting some high calorie toppers on it, to get her some extra fat. But now she will just suck it off the kibble and spit it out. EVO is a little to expensive to keep throwing her meals away because all she does is suck the good stuff off.
So now what i am doing is feeding her just kibble and if she eats all of her meal she gets half a BP sandwich. And if she doesnt' eat all or any of it she doesn't get a treat. She will sometime skip 1-3 meals before she will eat everything. Is this the proper thing to do? I want her to gain weight but i don't want her to develop bad habbits and make her more picky!

Any suggestions!!!

Dogs won't starve themselves..

Give her whatever you want to give her..put it down for 30 minutes..if she don't eat it..lift it..give it to her again a few hours later..if she eats it then great if she doesn't lift it and then give her it the next day..

Don't pander to her..

Trouble is, you want your dog to be in optimum health...I`ve got a skinny dog - I`m giving her breast of lamb in the morning (which is quite fatty) and Arden Grange (which she loves) at night. It`s taken a year to find foods that both she and I are happy with. I think it`s all trial and error - finding out what they like and also what suits them. Personally I wouldn`t give her treats like that because she won`t associate them with finishing her food - she might just hold out for it!
Remember though - it`s better (more healthy) for her to be a bit lean than a bit plump.

That is what i currently do. I leave it for 30 min and take it up. I do the same thing both meals.

Update,
Good news, i stuck to what i was doing and she is finially eating. In the last 4 meals she has eaten everything i gave her except for on meal she ate half. But progress is progress!!

Weird thing i found if i feed her in the bath room she will eat her food. Must be less distractions..