Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Phoebe is having this problem with her vulva.
It's certainly possible that she may have a issue with her bladder and that she's developed bladder stones again although it's also possible that she has vaginitis which isn't related to her bladder at all. Without a urinalysis, we may not know for sure but I do have a few suggestions which may be of help.
1. Gently clean her vulva several times a day with over the counter dilute, over the counter Betadine or Iodine to the color of weak tea.
2. Gently wipe her vulva after she's urinated with a warm wash cloth or non-medicated baby wipes since urine can cause burning or stinging of inflamed tissue which may worsen the problem.
3. Over the counter cortisone ointment can be applied to the area several times a day which may help reduce inflammation. It won't be harmful if she ingests a small amount of it but it won't be absorbed if she does. So, I'd distract her for 10-15 minutes after it's applied.
4. Vetericyn Spray is another good product to use in this situation and can often improve healing for any number of skin issues. It's available at many pet/grain stores or online.
5. Cranberry products aren't likely to be terribly effective if she has already developed a uti but may be somewhat helpful; I usually suggest them to prevent recurrent issues. Craninadin is one such product which I recommend.
6. As long as she's not vomiting nor currently taking any steroids or nsaid medication, Aspirin can be given which may help to reduce inflammation and can help with pain/discomfort. The dose would be 10 mgs per pound of body weight twice a day, with food to avoid stomach upset.
7. Encourage fluid intake which may help to flush out the bladder if she does have bladder issues.
If her vulva continues to be red and inflamed and/or she continues to behave as if this area is troubling her, then a vet visit may be prudent so that a urinalysis can be evaluated.
I hope this helps. Deb