I think that having a DX this time around could help a lot, even though you've been doing it every year, now you probably have a better understanding of WHY she behaves a certain way at certain times. For me, that makes a world of difference! Not that I don't get frustrated anymore... LOL but as they say, knowledge is power!
This is my opinion... when it's my kids (and me!), I continue medications during vacation. I have ADD/Inattentive Type myself, and I know that even though no one on the outside has any idea I even take meds, I can totally tell how I FEEL, and it's a huge difference between being stressed out and unable to enjoy things, and being relaxed and more patient and, well, able to enjoy things! It's not just about how well they're able to behave, I think it's often missed that there is a whole universe of feelings going on in the ADHD brain, only some of which are even manifesting in behavior. If the medication helps her during other experiences like school or an outing, it will help her enjoy her vacation, too.
(Slightly OT, but this was a game-changer for me, when DS2-the first of 4 out of 5 in our family to be DXed, was just diagnosed and before we decided to try medication... I was talking in general about learning what makes us tick and figuring out how to do the things we need to and the things we want to so we can enjoy our lives, and he told me he's not enjoying his life.

Honestly, I never would have known that, he never talked about being unhappy. But living with ADHD was stressing out his poor 7-year-old self more than anyone knew. The emotional component of the disorder took on a whole new meaning for me then!)
In general, I've read (this info, specifically in the ADHD magazine from CHADD... I'm totally blanking on the title of the publication! ADDittude? Ack!) that one way to tell that the dose of the medication is the right dose for you is if it lasts the duration it's supposed to. I take Vyvanse, and I realized at one point that it was no longer helping me 10-12 hours anymore, rather wearing off by mid afternoon... that was a sign I needed to increase my dose, which totally helped. I mention that because you mentioned looking into a "bridge," so if her meds aren't working as long as they used to or as long as they're supposed to, she might need to try a higher dose.
As far as strategies to enjoy park time, of course a lot depends on the kid, but I would guess that some of the most common triggers are having to wait on line and not getting to ride what they want, when they want.
To that end, you should know your kid: a touring plan might not be the best idea if she "wants what she wants when she wants it" and might melt down if you have to do what the plan says rather than ride X ride 3 times in a row. Or, she may utterly thrive on that kind of structure, maybe even would enjoy being in charge of following the plan and keeping watch of the clock-that's a stimulating activity. Two different ways to look at it, totally depends on your kid!
Waiting in line will happen anyway, and we've enjoyed following the Hidden Mickey book. I'm sorry to repeat if you're already familiar, but after going every other year since 1992, I only just found out about Hidden Mickeys in 2011

The Imagineers "built" Mickey's head/ears icon (and sometimes other character shapes) into the decor and architecture all over WDW, not just the obvious ones, but ones meant to be more hidden, such as the pupil in the eye on a mural, or a scrollwork on a veranda. The book goes ride by ride, helps you make it a game with points, gives clues, and covers the queue as well as the ride, restaurants, etc... if there aren't a lot on the queue you can be looking ahead to what to look for on the ride. We had a blast with these, I'm very excited to have the 2013 book!
I also just picked up a book for our upcoming May trip (the first since all 3 boys were DX'd, this should be fun!

), I think it's called something like "While Waiting In Line" or something like that, located in the same section as the Hidden Mickey book at Barnes & Noble, if that helps

, this one has more of a trivia/treasure hunt theme. It asks, for example, what creature is peering over the carpet at the Aladin ride? (monkey, camel, etc... 4 multiple choice) What is it wearing? (a hat, jewels, etc...). Then it goes on to the treasure hunt, which gives a list of items to check off. In Pirates of the Carribean, you can search for and tally how many lanterns there are (and it's queue-specific if you right or left). This one is new to us, but I'm very much looking forward to it!
In terms of waiting, if you can utilize Fast Passes to reduce wait times, as long as she's chill about visiting those rides when the time slot says, they can be a big help. There are also a few different smart phone apps that give wait times, that may help as you go through the day. I know there are threads on those in different forums.
Other ways to keep her occupied might be give her a small journal that you wouldn't mind carrying (if you carry a bag) and encourage her to write about what she enjoys, observes, wants to remember, etc... if you think she'd enjoy that. Or, give her a camera so she can be snapping photos or looking through the ones she's taken while waiting. It might be worth asking her if she'd like any of these things (if they are alright with you, of course). Perhaps starting a collection such as pin trading or pressed pennies could keep her occupied-again, that depends on many things including how responsible you feel she is if she might lose what you've invested in.
I know I'm throwing a bunch of "stuff" out there, but I find it helpful to have something that stimulates my kids, that increases the odds that they'll have something to focus on at a time when they'd likely melt down if left unoccupied.
Hope something here helps!