Granted whenever I say to hot salesgirls, hair salon girls, etc in conversation that I am going to Hawaii they all say "Take me - please!" and my paying for the trip is all they expect.
However, this is an SP/client thing and the OP has only seen the girl twice.
If he was a long time regular og hers the SP might just go with him just for the free trip and wining and dining. I say MIGHT so militant SPs on the board who yell "It is work! and I'd rather go alone" I'm not talking about you lol. I'm talking about adventurous young SPs with no bf or SO who haven't travellled much if at all. I have gone on trips and only paid for the trip, no fees on top, even had the girl refuse money when offered on top after the trip was over, so this does happen if the connection is right and if she actually enjoyed herself.
Anyway, he has only seen her twice, and the 19/56 ages COMBINED with the fact that the OP said his goal is to have sex when and where he wants makes this a paid trip. If she goes for free you have to treat her as a gf and can't say "Here is today's plan: we'll be doing it on a surfboard at 1pm, then on the beach at 6pm, then on the balcony at 9pm".
So fine, she likes the idea of a trip, the OP has the cash to spend, and a list of what he wants to do and where he wants to do it. Sure, it will be fun getting a bbbj driving a mustang (just don't drive off the road lol). Ask her what she makes on average in a week here. Some SPs make nothing one day, $200 the next, maybe $1,000 the next, maybe have a day off the next. So the fair thing, if you are paying for the trip and everything during it, is to pay her not the maximum she might make working full time all day every day, but what she actually does make in any given week on average. Pay her that, no more, no less.
For example, one agency girl on Terb works 3 days a week from 1 to 5pm at $250 an hour. So IF she filled every slot that is 4 hours per day @ $250 = $1,000 X 3 days is $3,000. Of course the agency gets a cut, so her after agency take home would be less than $3,000 per week, more like $2,400. That is what would be fair, so long as you pay all expenses AND she wants to go to Hawaii.
Of course if she makes more than $2,400 on average a week, you pay more, but she may make less than that too. Ask her.
Have fun! If you are going to Honolulu you can PM me for advice on things to see as I've been multiple times.