First of all, prayers for you and your family. Losing a loved on this time of year is especially hard.
However, I know her daughter will be absolutely THRILLED with the quilt!! Both you and your sister did awesome work!! And you're right - no one will notice any pleats or puckers or tucks, especially once it's washed a few times. You did exactly the way I would have done had I been given this task. And now you know what to do if someone else brigs you something like this.
Beautiful work, just beautiful!!