@Yolande96 yes, this is a tough situation and I am afraid your only option to (almost) assure a good review is to refund in full.
Since she has reached out to Airbnb with this lie, she is obviously expecting a full refund and is willing to get it at any cost. She’s already unhappy.
My personal policy is to never buy a review but I’m also fortunate enough to have many so one bad one can’t hurt me.
As I see it, you have two options:
fully refund her and expressed to her that you’re new to this, this will be a huge financial loss for you but you just want her to be happy. Basically just shower her with pleasantries. Even that won’t guarantee you a positive review or any review for that matter but will make one more likely.
Your other alternative is to stick to your guns, tell the representative that it is not true and that she simply wants to shorten her stay due to work circumstances and send a picture of your exchange with her where she states that. She then may or may not give you a negative review. Not all people leave reviews. Even if she does, he will have a chance for rebuttal or perhaps getting it removed if she breaks a review policy.
I know this is not really and advice but rather food for thought, but I’m hoping it’s helpful.