Your block is beautiful. And while I possibly would not have chosen those colors, they work well together, and I would be anxious to see the finished product.
One thing quilting has taught me is that I should never past judgement on combinations, colors or patterns until I have seen the finished product. I am very frequently pleasantly surprised by the vision of others. Sometimes we must just take a leap of faith and proceed.
Good luck and know your sister will love it.