Hi H.,
I have a suggestion-I am trying to learn to be organized and I do the FlyLady thing. In her "Control Journal" they have a section about a "family Yellowpages" in this area they have any pertinant phone numbers-including Dr, playmates, and Poison Control- numbers You may have already compiled to have in one place, print out a copy for her.
Include at the top of the page: HER ADDRESS, in case she has to call 911-if she is upset she might have to think about it.
Also, put in this list a set of her usual routines and foods she likes (she likes Bananas for snack in the morning, or whatever). Also, if you have a regular meal plan at home-include stuff like Monday is "Crock-Pot" night, Tuesday is Spegetti, etc...
Also, if you want to do this, tell your cousin that it's not a criticism of how SHE does things, just some idea of what your daughter is used to-she won't have any issues with her until after the first few days and if she Knows your child's routine/favortie foods and what she is used to eating, if you have special nights for things, she will be better prepared.
For your daughter, give her a picture of you and your husband and if you have anything you can record your voices on, do it-tell her whatever (We Love You, Miss you etc...) then if she misses you, your cousin can show her the pic and play the recording of you and her Daddy.
This is what I came up with, Hope it helps!
C.