my dog continues to chew her pads off her feet / IMAGES / please help!! :(

[Barbaraann]

All this time I thought my 7-yr old Golden, Annie had cut her foot, now I'm not so sure. She had a bladder full of struvites over 6 mos ago and has been on Royal Canin SO since. Two thumbnail-size remain. Many bladder infections and now we are trying Cipro prophylactly.She has hip dysplasia and on Rimadyl and glucosamine/chondroiton. Her pH is always high and is currently at 7. Distilled water does not bring it down. The diet causes her to gain weight and she is 121 lbs and should be 85. She was on Hills RD prior to struvites for her weight. My vet does not know what to feed her to allow weight loss and not cause more struvites in the process. Royal Canin says not to use SO more than 6 mos. Vet says stones are not completely dissolved. I feel like I'm between a rock and a hard place. I'm wondering if this is part of the foot problem that has just developed 3 weeks ago. I've been all over the Internet looking for information. All blood work is noncontributory and my vet thinks heredity may be a factor. I live in Tallahassee, Florida also known as "allergy capital" for humans and pets and we're in a severe drought currently. Any ideas? Thanks.