Help! Vaginal pain with no known cause?!

Hi, so my sister has been going through a lot lately and I’m trying to do some research to help her. She has been having very bad internal vaginal pain, and now visible swelling. She has been to the gyno and all of her tests have come back clean, no infections, diseases, or abnormalities besides the inflammation. She has been experiencing dryness as well and she is in her twenties. I just feel so bad, she’s really upset and in a lot of pain and doesn’t know what to do anymore. Has anyone experienced anything like this or know what it could be?

She has another appointment with the gyno in a week, who original gave her a topical cream to use which actually caused more burning.