It's possible she has a vaginal infection or a urinary tract infection and with her licking and chewing she is adding more bacteria to the area. I would take a urine sample in for testing. If you can get one from first thing in the morning that would be best. If the urine checks out then she may need to have a vaginal swab done to check for infection there. Any type of bacterial infection will need antibiotics. Keeping her clean and wiping the area can help with irritation but it will not take care of an infection.