Thank you for your query.
I hope there is no reason to worry.
It is difficult for me to diagnose the case without seeing the area.A photograph would have helped.Yes, thrush can be bad.The surrounding lesions maybe 'sattelite lesions".The other diagnosis can be genital herpes
which initially develops as small vesicles and then ruptures and forms ulcers.I think she will need an oral antifungal
once a week if she has thrush or might need antiviral
creams if she has herpes.Kindly consult a dermatologist
if the problem persists.Hope this answers your query.Merry christmas.