What a wonderful thing for you to do! Your quilt is absolutely Beautiful! I think I would purchase the yard of fabric and work it in With the others, if it's one of her favorites why not. That is me, But totally up to you. Either way I am not convinced "mother" was intending harm,I know a lot of quilters/piecers that are unsure of what colors may be liked when putting a quilt together and feel she was just suggesting what her daughter might like more. My opinion of course. I think she would be thrilled with whichever and whatever quilt you decide to make. I applaud your endeavor and be sure and show us pictures of all of your beauties!