seems to me you have two options: cave in, or call her bluff ...
Prognosis is not too good for service - she's clearly feeling entitled, and feels men owe her a debt of gratitude. My guess is you'd get a much more dependable service spending that much on 2 HGs or 3-4 walkups ...
... but then you wouldn't be fuelling your fantasy of nailing a 19yo student!!
Admit it, it might be worth it just to tick the box
and my hunch is there are indeed a long queue of guys willing to pay 1500 once for just that experience.
On the flip side, if you say "thanks, sounds like we both have some alternative options, let me know if you change your mind", or maybe offer her a bit more for the overnight ... she might just get back to you. If she did, the prognosis would be excellent ...
At this point the only other way to handle it would be to switch to good-natured humour, and maybe try to build up a rapport without any pressure to decide either way. Maybe praise her for being so desirable, how you'll look after her as soon as your boat comes in, etc.