By the time you go through all the trouble of cutting the tissue then getting it "fixed" onto printer paper or spend the time also cutting the freezer paper just to send it though your printer you have in fact wasted more time than you would have spent by just tracing the pattern onto a full size piece of tissue paper.
Plus if by chance you get even a tiny little drop on the printed paper you are going to ruin your quilt. The printer ink will RUN all over the place if it gets wet.
I think you sister in law has the right idea, although it seems time consuming I think it is the best way in the end. However I too would be wondering if there were an easier way to do it. I just don't think there is.