First, depends how well you two know each other and how well you get along outside the bedroom.  Is there a friendship there to build upon?  Common interests?

Second, what kind of vacation?

It is not unheard of for a lady to consider the vacation (all covered by the guy) to be adequate compensation, but I would strongly suggest communication in advance is critical.

I have done it and it worked out very nicely.  I always paid her a fee, but always specially negotiated.  I have one upcoming next spring where the fee is already known to be zero but there are some extenuating circumstances.

It can be a very rewarding vacation to the right place with the right lady.

If you are going with other company, you may want to take into account any issues that might arise with any company you have.

I would be straight forward with her to clarify that she does not want compensation, how play and private time will work, and the expenses you will be responsible for.

You also need to clarify on if she plans to "work" while on vacation by putting an ad somewhere and what are the ground rules. In essence she could be covering her touring expenses on your dime.

It all depends on well you know her, work out all the issues and pit falls in advance.

It could be highly discounted ($1,000/day?), but you'll both have a better time knowing that there are no strings getting tied in the situation.

Remember also that providers don't get benefits like paid vacations, so her time should be compensated somehow.

Think of the fee as an insurance policy against emotional damage.

I presume you two have spent some long sessions together and are sympatico.  That goes without saying.

If she is a good fuck take her along. Whats the down side.

if she wants to go and you are willing and able to take her then go ahead.  However, if you are not comping her then book a room with 2 beds.  I mean the cost of the trip and expenses are apt fee for companionship and sharing taking in the sights with a sexy lady as your "escort" without the addition of any sort of sexual gratification.  You should talk to her and ask if she needs a daily fee for consorting with you, or if you can work out hourly meetings throughout your time together.  

It could work in your favor but if you make her feel like she should come on the trip AND provide you sexual favors continually during the trip you are likely to loose a friendship and perhaps even attain a bad rep in the community for taking advantage of the situation because things were not clear to you in advance.

The other possibility is that she really likes you and you are friends.  I have done this before where I told a very trusted guest about a trip and even booked him in.  We had a great time just hanging out, though I did pay my own way and had my own way.  However, nothing further happened but it is ok to hang out with guests and vice versa if everyone involved is on the same page and getting what they need.

Friendships with providers are simple.
Just keep the private/professional lives separate.

It's dating that I hear is difficult.
I have no experience there.