Okay, gotta first say I adore this happy little quilt, from the birds to the colors to the fabrics to the piano keys border. Your little granddaughter is going to love it, love it!
Here's what I'd probably do if it were my quilt. Keep in mind, I don't have a whole lot of experience, but one thing I've learned is that to get better, you have to practice, and it's a lot easier to practice with bravery on a child's quilt. SHe will love you and never even notice the flaws. She will see how cute all your thread drawing is.
My plan as I'm looking at it now:
1. Echo around the birds in such a way that it makes a heart shape (not around the outside of all feathers. That way, a heart will show up in the center of the back. Fun for a child (and adult!) discover . Then straight line around the edges about 1/4 inch in (not in the ditch). Think "box around the heart".
2. Make one big daisy in each big white square. Box it in.
3. Do those crescents from corner to corner (see nativetexan's picture) on just about all your triangles. The curves add a gentle look to the hard lines of squares and triangles.
4. In the border, wiggly lines side to side in each dark fabric. Connected hearts and flowers in the white ones.
I like to practice on paper first, and mark my large designs with Crayola Ultra Washable markers on the quilt before I start.