What a precious panel. Yes, Spoonflower.com does wonderful work & IMHO isn't that expensive for something we can't do by ourselves. I used them for a crossword puzzle and clues on my MIL's 90th BDay quilt here:
Appliqued Memory Quilt for MIL's 90th
Unfortunately I don't have any quilting suggestions but want to say how beautiful your DGD is and what a lovely memento this will make for her. I hope you will post your finished wall hanging for us to see.