Question: My lease is up this summer and I'm planning on moving apartments. The problem is that I also have a 3-day trip scheduled to start the day my lease ends (cannot be changed).

My cat will be a little over a year old at that point and has always lived indoors at my current apartment. When I go on trips, I usually have a cat-sitter come to the apartment. I've only boarded her once, just for the day, and she took a few hours to return to normal after coming home.

I'm concerned about her reaction to moving to a strange new place, especially if I were to leave immediately after. What is the least bad option for her?

1. Move a week or so early, leave her there and go on trip (avoids boarding, but is that enough time for her to get used to it?)
2. Board her, move, go on the trip, and bring her back to the new apartment afterwards (or would that be doubly traumatic?)

Answer: 
I did the exact same thing once, I moved out to a new apartment with my cat and there was an emergency at the day I was moving so I had to leave for a couple of days.

What I did was; I confined her to a smaller room full of her favourite things & furnitures. This included my bed (she always sleeps with me), her toy collection, her favourite blanket which she sometimes kneads and cleans, a couple of my clothing, food, water and of course a closed litter box. Since she was surrounded with familiar things & scents she had an easier time to adjust (which I have heard from my friends who kept an eye on her basic needs a couple minutes each day). And when I returned she was pretty much normal but I had to go through the skittish behaviour when I introduced her to the rest of the apartment.

If you can bring her a week early; by all means do it. Your cat will probably adjust in that time frame.
I agree with the cat whisperer. Take it there at least a week early. If you can't, then bring it for short sessions to get used to the house daily, and confirm with the current resident. If you can't cancel the trip, get a family member or someone the cat knows well and is used to to replace you and introduce it.