I hear you! Changes to routine are always difficult, and it's amazing how long it can take a little one to get back on track.
I have to say, though, that I think you just have to try to roll with it the best you can. It's so good for her to see your parents and Gramma and spend this time with them. Life is too short, and I do believe that kids need to learn how to deal with adjustments to their routines.
When you have them visit, try to spend a little extra time with her alone before putting her down to sleep. Read extra books, sing extra songs, etc. so that she's relaxed and sleepy before you put her in bed. She may even forget that the company is in the other room!
Traveling isn't easy with a toddler - my son loves sleeping in his crib, but nowhere else right now. All I can say is to do your best to make the sleeping environment as similar to home as possible. Have your baby watch you put her bed together, and spend time playing in the room when it's not bedtime so she can get accustomed to her surroundings in the daylight. Load up her travel bed with anything and everything she has in her crib at home, bring a nightlight and a white noise machine if that's what she's used to. She may still resist and have a hard time, but it will make it loads easier.