i can tell you that my hubby showed up unannounced at my son's (21 m) daycare friday, which i was surprised and a bit dismayed at...but the sitter said they had a good cuddle, lots of hugs, a bit of tickling, and when daddy left, my son was a-ok. wierd! i figured he'd have had a huge fit. sometimes they surprise us! i would definitely get her used to "i'll be right back!" or "see you soon!" or another phrase when you're leaving to tell her you'll come back, that helps with my son. also i might leave a picture of yourself behind for in case it gets tough for her.
another thing to keep in mind is that two year olds don't feel/see/understand time the way we do - if she's used to staying the night at grandma's, it shouldn't be hard for her. my son stays the night at grandma's about every other weekend, sometimes more, and when my sitter was off a couple weeks ago my mom took him for three nights, and he was fine. VERY happy to see us when we picked him up, but fine!
you didn't mention how long the trip was, so more than a few nights, i couldn't tell ya. but just keep a good attitude when leaving her, reassure her you'll be back, and that's about all you can do. don't stress out about it or be all keyed up when you drop her off or she'll pick up on that and it'll be much worse.
good luck and have a good trip!