It wouldn't do her any harm to try miconazole or whatever anti-yeast med you happen to have. Do you have any questions about dosage and timing? It's not disruptive to her system like an antibiotic, only targeting any yeast that may be there in her system. If there is no yeast, it's benign to her system overall.
I have been reluctant to agree that she could have a yeast issue because of her young age, but anything is possible. I would do a twice a day, seven day treatment and see how she does. If you want to wait until you see how she does on the egg and tofu, it's your call. At least now you have a couple of things to try, none of which will be a shock to her system one way or the other.
I'd reserve the vet visit for after you try these measures, if it's determined that they didn't resolve her issue.