Beautiful quilt! Your "sneaking" it past your sister reminds me of when I was making two Raggedy Ann dolls for my nieces (who were 4 and 1 at the time).
My sister's face when she watched me work on them told me I had to make one for her (she was 15 at the time). It was a delightful shell game that got tense only once - I was embroidering the chest-sized heart inscription "[Wunder-Mar] loves Pea" (my nickname for her) in the car so she wouldn't see, and she walked right past the car without noticing I was even there, doing the last stitches on her (nick)name. (whew!)