Hi, it seems as if she is trying to get a refund. I had a similar situation with my second airbnb guest as well, I had given the discounts airbnb suggests, at the time I gave 20% for the first 3 guests and 50% for montly stays (didn't know airbnb would join both discounts) guest ended up getting a 70% discount for the month. Huge mistake on my part... Had a lot of complaints during their stay, said that it was unberable to stay here (I've only had 5 star reviews before and after him) and after about two weeks said he wanted to leave and wanted me to refund him. Kept insisting and complaining. Told him he could leave but there was no refund. He aplied for it, but he had no base so it was refused. He ended up staying until the end, and funny enough gave a 5 star review. I was dreading his review... Some people will do and say a lot to get a refund, they want a free Holiday.
Since she already left you a review what I suggest is very polite and professional (no emotions) answer to all her complaints in your reply. Go point by point... Start with an apology, so that future guests can see... something like ...
" Hi X, I'm so sorry you had problems during your stay, we strive to give guests the best experience. The cleaners had assured me that they had cleaned everything, but I will ask them to be more careful so that they don't leave any dusty spot. As for the cleaning fee we try and charge as little as possible, we do have one of the cheapest rates around here. Since you were arriving at midnight, two hours after our check-in time, we though that sending you the entrance code before your arrival here would be enough but we will think about sending it a few days before from now on."
I'd say something o those lines. Future guests will read her review, but also your reply.
Don't be too afraid of negative reviews, you will eventually get them. It is how you respond to them that matters.