I have made quilts that I absolutely hated during the piecing stage - sometimes I get all the way done and still hate it - but then I wash it and iron it and sometimes it comes around - I start to love it - the moral of the story is - I reserve judgement until I am completely finished - besides some one out there will love it.
BTW, I love the block you posted - and your sister loves it - just think how thrilled she will be when its done - then you will love it for her. Yah!!!