This might be a diaper rash
secondarily infected by bacteria.
You may apply antibacterial ointment like T Bact thrice a day for about 5 days.
Avoid diapers till it heals.
Do not wipe hard. Gentle mopping with wet cloth will do.
increases or the lesion becomes big or painful for your baby, do see your Pediatrician
. In such a case she might need oral antibiotics
Hope my answer helps you.
Wish your daughter good health.