I recommend Dr Shawn P Messonnier at Paws & Claws Animal Hospital in Plano, ###-###-####. I used to work for him, so think he is really good, but have also seen him help a lot of animals using holistic therapy and/or conventional therapy. I had a Boxer myself with terrible skin allergies and did all the allergy testing and shots, which did not help, and decided to give Dr M a try on my dog to convince me that holistic therapy might work. I was astounded. My dog had open, bleeding wounds on her from the allergies, and within a couple of weeks she had healed up. He used acupuncture on her, and from then on (she was two years old) she never needed any more treatment for her allergies. (She was euthanised at 12.5 years old having never had a recurrence.) Bichons are known to have problems with allergies, poor things. They are really sweet dogs.
As for the bladder stones, have they been the same both times she had surgery? I'm guessing it was calcium oxalate or calcium phosphate stones, but I do hope they checked both times to make sure. There are several brands of prescription food you could use: Hill's Prescription diet, Purina CNM, Select Care and Waltham - but it totally depends on what kind of stone(s) she gets. If one food doesn't help, try another - BUT UNDER THE SUPERVISION OF A VET. If you chose to go to Dr M, ask him about this as well.
I have, since leaving Dr M, moved out of the country and taken a degree in veterinary nursing, and in my experience, bladder stones (uroliths) are not that common on dogs in comparison with cats. And your dog, having allergies at the same time, can be a difficult one to treat because the food to control the stones could exacerbate her allergies.
Best of luck to you! I know how frustrating it is to have the greatest dog in the world with health problems.