I decided to make a "Grandparent's Allergy Information Pack," and had it arrive a few weeks before we did.

I had also wanted to include some information on how to properly read food labels for her specific allergen. I was a little surprised when my best source turned out to be the USDA. They have handouts specific to all food allergens and they are wonderful for teaching how to read food labels for a specific allergen. They call them Food Allergy Fact Sheets. You can find your specific allergen with a straight web search. This is the Peanut One, USDA Peanut Food Allergy Fact Sheet.
After putting this packet of information together I sat down a wrote my Grandmother a letter. I wanted her to understand that we did not expect her to remove all peanut products from her home, but for the time that we were there could she please put them up out of reach, we suggested above counter height for safety. I asked her to please not feel overwhelmed by the information provided and if she had any questions or concerns to please call me and I could walk her through it. I relayed to her that we simply wanted her to have an understanding of what special needs our daughter required to be able to stay with us at her home. I told her how much we have been looking forward to this trip and how we just couldn't wait to see her. I know she had been dying to squeeze a grand-baby for a while.
I waited until a few days after the package had arrived to call and see how things were. When I asked about the package she informed me that not only had she received it but had read it all. She said that it was very helpful and that she learned so many things that she would never even have thought of about having a food allergy. She told me that when we came our daughter would not find anything in her home. And to put the icing on the cake she asked me to e-mail a list of our daughters favorite safe snacks for her to have on hand when we arrived. I knew there was a very good reason I love this woman so much. Then she informed me that because I had sent extra pamphlet's she intended to pass them out to anyone who would be coming over to her house and letting them know that they can not being our daughters allergen into her home.
* If you live near to you parents/grandparents and they help to watch your child I recommend that they have a safe snack box at the grandparents, that is just for them.