Evita,
Your girl is lovely and these a very nice photos of her. Since you asked, I'll offer some constructive criticism. It seems to me you're too concerned about the technical aspects of your images and too little concerned about getting your subject to look her best. Doing portraits by yourself is difficult because you both have to handle the camera and bait your dog. I've learned to be able to handle the camera with my right hand and my "bait" -- whether it's food or a toy -- with my left. Or, you can use a tripod. The whole thing about pet portraits is expression: getting your dog to look the way she looks when you say to yourself "gosh, she's just beautiful!" A squeeky toy will get that expression and get her ears up so she looks as beautiful in the pictures as she does when you're not taking her picture.
From a technical standpoint, when you have a dark dog, try to put it against a medium background. Personally, I use black even with my Rotties but I have studio lights and I know how to pull them off of the background. But if you balance the color of your dog against a medium colored background, you'll not risk blowing out the background or under-exposing your dog.
Here are a couple of examples: first up, our Golden, Crash, in an informal shot in the yard.
Notice that his ears are not plastered back and that toy is so "him" I had to let him hold it.
And here's a studio shot of our oldest girl, Cassidy Ann, in my preferred low-key style. Notice how alert she is and how she's responding to my "rude mouth noises"
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So, my advice is to concentrate less on the technical aspects and more on getting that expression from your dog that you love so much. And have fun. If you're not stressed out about the photo session, she won't be stressed out either.
Jim