It is horribly stressful. Hang on in there. I'm not sure exactly what you need to help you. The thing that springs to mind is that she is claiming you bullied and harassed her. They are quite distinct :-
Harassment applies to targeted unwanted behaviour specifically relating to a protected characteristic (sex, race, disability etc) In the investigation, she will be asked how you harassed her specific to a PC (e.g. You targeted her because she is Muslim, you were derogatory and discriminatory because she has a physical or mental impairment etc)
Bullying - she needs to elaborate specifically on how you bullied her, which normally equates to some unwanted, undesirable negative behaviour targeted at her personally. She would need to be specific about how it affected her and whether it was one or more than one occasion (date/s time context) It doesn't require witnesses, but balance of evidence that shows consistency I.e what is the likelihood it is something you would do to her personally but not to anyone else.
Hearings/investigations are designed to ensure both sides have an equal say. Get your ducks in a row. Make a log of times you and she had had any such situations that might have led to her grievance. If you believe it was the other way round, pull together your side of the story.
Best advice I have Don't rely on memory, it will let you down Facts and data, keep it succinct and crisp, to the point.