Elderly woman with a linear cut in vulva - what is it?

Need advice for my grandma. She is 68. A few days ago, she noticed an approximately 5 cm long linear cut in her vulva. She has no itching, no pain, but it burns when she goes to pee. There is no redness, but that cut or irritated line looks red. Any idea what this could be? (Obviously, she is sexually not active.) I am really worried for her