I'm not saying doggie is in grave danger -- just that more care should be taken given the type of epithelium that is infected and the relative pathogenicity of the likely agent.
I'm answering mainly for my own learning curve, but here's what Hirsh et al. have to say in Veterinary Microbiology, 2nd ed.:
Quote:Candida albicans is associated with mucocutaneous areas, particularly of the alminetary and lower genital tract, of mammals and birds.
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In dogs, candidiasis produces ulcerative lesions in the digestive and genital tract. Rarely, dogs develop septicemia with lesions in muscle, bones, skin, and lower urinary tract (especially those with diabetes mellitus).
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Disease is linked to immune and hormonal inadequacies, reduced colonization resistance (a measure of the "health" of the normal flora), or intensive exposure of weakened hosts or vulnerable tissues. These conditions account for susceptibility of infants, diabetics, subjects on antibiotics and steroid regimes, patients with indwelling catheters, and mammary glands of lactating cows.
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Correctin conditions underlying clinical candidiasis may in itself lead to reovery. ... Fluconazole (preferred) or flucytosine is useful for treating dogs r cats with lower urinary tract candidiasis.
Now, it doesn't seem like there's even a confirmation that there is a fungal involvement. It's very possible that the bacteria involved are simply not responding to the antibiotics. Did your vet submit swabs to a lab for culture and sensitivity testing? There may be a bug present that is resistant to whatever antibiotics are being administered.
Or your instinct could be correct, and the antibiotics are clearing out the normal bacterial flora of your dog's vagina and making way for yeasties -- a condition that would be further facilitated by your her signalment (an old dog should usually be considered immunocompromised) and the preceding bacterial infection (damaged tissue is far more susceptible to infection than is healthy tissue).
(Not questioning your vet, just chattin.')