She is experiencing anxiety. The "elephants" are a concrete way that she can express that to you. When she says, "There are elephants in my crib" she is saying - I'm scared and anxious. All children become scared and anxious at times. Hopefully nothing worse than a loud elephant happened to her on that trip. I always wonder when kids show on-going anxiety if something else bad happened to them around, close to, or during the time that they experienced the "elephant" or whatever it is that they are complaining about. And she just associates "bad and scary" with that elephant because it is something concrete that she knows how to complain about. Three year olds don't know how to complain about anxiety - they just experience it.
She also may just not want to separate from you at night (or find herself alone in the morning when she wakes up) because she is away from you all day as well. So she may be expressing how hard that is for her. Is she comfortable and close to the person that takes care of her during the day?
My step-son is almost 9 years old and when he experiences anxiety he says that he sees spirits or ghosts in his room at night. When his anxiety seems to calm down, he wakes up less at night and he stops mentioning spirits and ghosts.
Remember that children don't have the vocabulary to express everything they feel and a lot of times an "elephant" is not the problem. Rather - they are just experiencing general fear and anxiety. She just experienced the elephant - knew that that was scary, and now when she feels scared she identifies it with "elephant."
My step-son's older brother was killed in a pedestrian/auto accident when he was 3 and the brother was 6 years old. Now whenever he goes through an anxious time (first day of school for the year, a lot of switching back and forth between mom and dad's houses, really any thing at all) he only can express his uneasiness, fear, or anxiety as "missing his brother." Yes, sometimes he misses his brother. But a lot of times I think that he just feels bad and identifies feeling bad with the first major trauma (which obviously was a truly major trauma) with losing his brother. So that's the only way he knows how to express it.
I doubt your daughter's anxiety is all about elephants or even loud elephants. She's just having anxiety - maybe from being away from you all day and then all night in the crib, or maybe from something else. I'm not trying to give a guilt trip about not being home with the child during the day. Just explaining how things may feel from her perspective.