Question for all the providers:  
If a client wants to buy clothing for a provider that they have an appointment scheduled for. Would you accept it prior to the appointment or only at the time of the appointment?

The only way I see this happening is if you are sending her a electronic gift card to purchase the lingerie herself and allowing enough time for delivery before you book an appointment with her. As for someone meeting up with you just to pick up some lingerie from you is asking a whole lot. Have you seen the provider before? If so you might want to bring it along and ask her if she could consider wearing it for you the next time you see her. She may also have a physical delivery address you can ask her about that she receives gifts at. But personally there is no way I'm taking time out of my busy day to meet with a stranger "off the clock" to pick up a gift. But then again I'm a busy woman so maybe someone who is not as busy wouldn't mind. No harm in asking but don't expect a favorable outcome.

If she doesn't have a wish list for you to buy directly from and the service ships into her ( delivery code, Amazon etc) then you're only other options imo are to send them an egift card or you buy it and bring it at the time of the date.  Maybe if you already knew the lady she would accept it from you prior to your appointment.