She could also have children or animals that need care while she is gone that long and that needs to be factored in for her. She may have a boyfriend/husband to leave at home and REALLY needs it to be a super amount for them to be accepting enough to deal with their lady leaving so long. Or maybe a square job that she would have to take off for. Overnight childcare from a non family member is NUTS! Don't forget even though they are travel days during your vacation, they are still days she could have been working a full day at home.
If those are not in play, I think making up her daily minimum requirement would be a must. If she's not able to answer her emails and calls while she is gone, that could be potentially be costing her money as well by not being able to book things for when she gets back. She could have a dead week following the vacation because she couldn't respond costing her thousands of dollars. There are a lot of behind the scenes things you probably wouldn't have thought of.
A suggestion, maybe you could offer to give her some time to herself a day to catch up on her emails/calls so she can stay booked for when she gets back? Maybe let her know how often you'd want to swap fluids and if it's not a high maintenance scenario,( i.e. in the bedroom all day long) it would be a bit less?
It's great that you have known her for awhile but thinking that might you get a discount because your ponying up for the high end vacay is probably wishful thinking. Our rent, car payment, electric etc all still costs the same no matter how close we get to a client.
I know guys don't want to throw down the top dollar on the first offer because they are hoping you throw down a lesser one but, if shes THE one you'd have the most fun with and the one you really want to come, just don't beat around the bush. Tell her what you can afford, an idea of what you're expecting, or not expecting and give her a couple of hours space to do emails/calls or just be alone.
If you don't have a set date/time that you're going already maybe ask her if there is a slower time in her schedule that it wouldn't interfere with her other appointments and maybe she'd do it cheaper to fill that void. If you guys have spent more time together and gotten close she could be comfortable talking to you with that type of thing. If you aren't that close, it may be insulting to her sooo... be careful =)
I've gone a few places with clients and that's what we always did. Go around a time I was usually pretty slow and I didn't stress about home appointments and the vacation was relaxed and reasonable.
Good luck and have fun!