I found the perfect fabric at Fabric Place, the local fabric store. I saw it and I knew it was exactly the right choice, so when they were having a 20% off sale, I picked up about 7 yards so my mom can make a crib skirt and valance. The fabric is "Sweet Dreams" by R Kaufmann. I also found a coordinating stripe that can be used as trim/border on both items.
For the sheets and bumper I'll just go solid green or yellow.