That is so cute! Does she know about it or is it a surprise?
I'm probably too late, but I'll still throw in my two cents.
The center is so graphic that I think a pieced border will compete too much with it. I would stick with either solids or something that reads solid (tie/hand dye, tone on tone print, etc). I would do two or three strips, and if you want to add another color royal blue or red would be nice. I'd only do a 1" or 1.5" strip so that it's just an accent, but some people don't like strong accents like that. If you have a couple of solid borders you can do the binding in a print or stripe, and since it's not right next to the center squares they won't fight.
Looking forward to seeing whatever you choose!