You are better off being honest and decline the service. If you dealt with an agency, call them up while she is there and let them know you don't intend to pay the driver's fee because of who they sent. If it is just a matter of taste, but she is who you requested, pay a courtesy amount.
If you don't you will get blacklisted and won't be able to use the agency again, and there is a very good possibility that your info will be circulated amongst the agencies. If you prefer outcalls, it would be in your best interest to be straightforward. If it is a novelty to you, don't expect to be able to do it again if you don't deal with it honestly. No reason to pay a fee if you call them back and complain, while the escort is still there, btw.