Her limits, set by her and stated first
Your therapist decides what a session includes, says where her limits sit before it starts, and those limits hold for the whole of the visit.
One person decides what a session includes, and she is not in the booking conversation while it is being written. She is deciding for herself which bookings she takes, and when she arrives she says in her own words where her limits are. Everything after that follows from what she said.
Stated before, not discovered during
The point of saying it at the start is that nobody has to guess later. There is no reading of signals, no testing of edges, no working it out as the hour goes on. She tells you, once, plainly, and then the session runs inside what she told you. Guests who have booked here before tend to say this is the part that makes the evening easy rather than the part that constrains it.
They do not move
Not for a longer booking, not for a larger sum, not for a compliment and not for a joke. A limit that could be moved would not have been a limit, and the house has no power to move one either, which is why the thread never suggests that it might. This is the flattest sentence on the site: what she said at the start is what holds at the end.
If one is pushed at
The visit ends at that moment and she leaves. The fee for the reserved time remains due and nothing further is added to it, and nothing is argued about on the landing. Writing it down in advance is the reason it cannot come as a surprise to anyone. The same arrangement is set out in flatter wording in the terms.