@Muslim4 Unfortunately you are going to encounter some guest that are never fully satisfied despite you bending over backwards for them. It sounds like you made the attempt to appease her by taking the reservation last minute, being present for her arrival despite her tardiness, and extending a discount.
The best thing you can do in these situations is leave honest reviews. This allows future hosts to be aware of potential behaviors or problems. Sometimes it also allows the guest to be more aware, as some individuals are oblivious to their uncleanliness or inability to follow direction.
Here would be my advice for last minute reservations. I take them on a case-by-case basis, and I am very specific about the check in time. This allows me to not feel rushed and assure the accommodations are ready. Before accepting I typically send the following message "Hi XYZ, thank you for your interest in my accommodation. While I would be happy to host you, given that it is a last-minute reservation I wouldn't be able to check you in till X time or between X-X time, as I need to assure the home is ready for your arrival. If this is ok with you, please let me know and I would be happy to approve your request. "
Everything else aside, price should not affect the accommodations standards such as cleanliness. Just because a guest received a discount doesn't mean they should expect or accept less than what is advertised.
In the end you have a right to accept or decline requests as they come. In the future if you feel someone is difficult from the get-go (Ex changing their mind constantly or not committing to the reservation) trust your instinct and decline them.