Sounds like a food problem to me. Are you sure no one is giving her "teats and scraps"?
Expensive isn't the way to pick the best dog food. You may get some help searching on a string like: "dog food and gas" I'm sure there are better inputs to a search, but I bet the one I offer will return some results.
In general a "grain free" is a good start on improving dog food - then one that claims to be very "digestible" - that may be a code word should not cause intestinal problems.
We use a kibble from Natural Balance and are now trying a similar from Natures Recipe. Both are fish/potato based and are grain free, and claim to be easy to digest. Our Westie has a cast-iron stomach and fine silk skin, he has some food allergies that show up as itch. Neither of these brands are "bargan priced" and I never see them in the supper market or walmart pet food section, but I'd not call them expensive.
As a side-note, my wife asked me last night if I could smell our dog, gas. I couldn't but she can smell a cigarette at 300 yards.
Thanks for replying to my question...I give her kibble so should i try the natural balance from kibble?? No one is giving her scraps i can't even give her bones it is bad on her belly....
I just switched to Natures Recipe in Salmon and Sweet Potatoes - again in a dry kibble form. I changed after using a 24 pound bag of Natural Balance mostly to give the dog some variety - Recipe also has higher salmon content and is rated a little bit higher on a respected dog food evaluation web. Recipe is also more available in my area, PetSmart carries it.
When a dog has an allergy skin or an intestinal problem one approach is to limit diet and see if that helps. If it does one can then consider trying a controlled introduction of other foods, if still no problem, then you have more choices on food.