I really like the journal idea but both of you need to write one. I forced our kids and myself to write ones when we holidayed/camped and rereading them is wonderful and can be very funny.

Ask her to prepare for the holiday too with ideas to keep you from getting bored. It might be interesting to see what she suggests. You could have a two jars to pick the activities. (one her list and the other yours)

Have fun and enjoy your time together.

I came up on an idea using a spin off of the Journaling she is not much of a writer. I will Print off pages on cardstock such as the kinds of plants and flowers we found (I have a wildflower identification book). The kinds of trees we identified, The Birds we saw etc. Along with taking pictures of those things then she can later add the correct pictures to the pages.

Never thought of your granddaughter thinking of things for you to do. excellent!!!
I want to hear all about your vacation with her when you come back.