When a request is declined, and why
A booking can be declined by the house or by a therapist, at any point and without a reason being owed, and the right response is a short thank you.
Not every request turns into a booking. A therapist may decline one before it is agreed or after, and the house may decline one too. No reason is owed for either, and none is usually given, which surprises people until they think about why.
Reasons that are none of your business, pleasantly
She may already be committed. She may not be working that evening. She may have read the message and decided it was not for her. An address may be somewhere she does not go, a length may not suit her, or the thread may have gone somewhere it should not have gone. Explaining which of those applied would invite a counter-argument, and there is nothing here to argue with.
The one right response
Thank the thread and leave it. Nothing further is called for. A guest who does that has lost an evening and nothing else, and is welcome to write again another time. A guest who argues, rephrases, offers more money or tries a second account has answered the question of whether a later booking is taken.
What a decline is not
It is not a bargaining position and it is not a hint that a different wording would work. Nothing about the phrasing of a refusal is code. Taking that at face value the first time is, in the plainest sense, the skill that separates guests who book here easily from guests who find it difficult. The FAQ answers the practical questions that come up afterwards.