Don't know if you saw the video of the lady that gave away quilts to the needy. Many of them she thought was ugly but they ladies that got them loved them. So keep plugging away and remember it's for your sister. You don't have to love the quilt, just love your sister!
P.S. I had a quilt top I started several years ago and it had laid in my closet but I determined to get all my WIP finished before starting anything new for the year. I immensely disliked the quilt and still do but I finished it. I know someone will love it, even if I give to a charity and that's what counts.