Not trying to be flippant. Have you asked her how much she needs (NOT wants) to do this?  

 
Assume you are paying for air fare, taxis/grabs, meals, drinks, some Vegas entertainment (shows, attractions, etc.) and shopping. And if you are, will you also be covering the same (or some) costs for her friend?  

 
Will her friend be joining any BCD time?  What is your all-in cost to accommodate these two?  

 
Expectations: Does she expect to get some type of hourly rate based on her current allowance? That will be a disaster! (ex: 400 allowance for a 4 hour date = $100/hr x 36 hours = $3,600.)  

 
Will she incur any costs by coming with you (missed pay from work, dog sitter, etc.)?  

 
My suggestion is to craft an offer something like this:  

 
1. Some multiple of her regular allowance each day (ie: 0.5x400, 1x400, 1.5x 400, 2x400) with the assumption that you will go BCD at least once a day. Plus,  
2. Some additional daily cash for "fun" she does on her own or at least without you: Maybe $100 a day.  And
3. Ony offer to cover her friends' costs (air, meals, drinks, etc.) but no more. Unless,  
4. The friend will join one or more BCD, and so should get an allowance 1x400).  

 
The other approach: If she is VERY eager to get an all-expenses paid trip to Vegas, you could offer to pay for real costs, plus some of the costs for the Grand Canyon trip and that's it. She and her friend get a free trip, and Daddy gets thoughtfully thanked for his generosity.

 
In the past, I have taken an SB to Vegas for a week while I was attending a business conference. It was her first trip to Vegas, and I left her alone day times while I was working. She got all expenses (only while I was physically with her) paid and about $100 a day for whatever. No additional allowance. The key to this was that she really wanted to go to Vegas.  

 
If your SB is going because SHE really wants to go, use this trip as a reward. If she is going because YOU really want her to go, you may need to make an offer to "compensate" her for the extra time, disruption of her schedule, and missed revenue opportunities back home.  

 
Life is good

 
The Cat

My SB really wants to go.  I have bought and booked everything already and she has not brought up any discussion of PPM.  She is looking forward to all the shows dinners etc.  In the past I gave her usual PPM for an overnight because I bought gifts dinners etc.  She was satisfied with that.  I am thinking of giving her 3x PPM.

Similar to Herb.

1. All expectations are on the table before leaving.  How much time she has to spend.  Sex.  Time with her friend.  Is she joining or just having breakfast the day you leave and she shows?
2. Schedule some time for you to hit the tables.  Maybe get her massage or nails.  Time alone is good.
3. Figure out what activities she wants to do and make a schedule.  
4. Find a cute gift for her.  She will love you for it.  Doesn't have to be expensive, just a good gift.
5. Fuck a lot

Thanks for the great advice. The time apart thing makes sense.

Ditto on what's all already said. The only thing I want to add is when I did travel or multiple days to a location and my SB talks about bringing a friend I made sure I'm clear about what the dynamic with her friend.

Is the friend a guy or girl?  
If it's a guy, then it's a no. I'm not sponsoring any of her guy friends. They can pay their own way. If her friend is a girl, then I want to see her pictures. If I find her attractive, then her friend needs to join us as a SB as well. Double girlfriend date basically. Otherwise, I'm not paying for her friend.

So an update.  Came back from a 3 night trip from Vegas with my SB.  We spent every minute together.  It was fantastic.  Rented a cabana the first day.  SB wanted to have sex in the cabana. Went to dinners and shows.  Did high end shopping.  Taught her how to play blackjack.  Sex was incredible.

At the end of the day, SB was fine with the high end gifts.  Nothing more. Of course I did give her some additional cash.