Boston, it could be a fun challenge for you and your sister to find blocks with only squares or rectangles in them. Or applique in them if that is your thing.
Or, you could gently be honest and tell her you need a bit more time before you commit to another BOM.
It looks like it was a very fun BOM. It's a beautiful quilt. With a proud beautiful smile holding it up.
What a fun memory with your sister.