Introducing, three quarter sleeve short cardigan for Mommy refashioned into a grandpa cardi for M.
Start with your cardigan inside out. I used one of her shirts for the pattern. Make sure the sweater is lined up correctly. And...
CUT! Once you have the body of the cardigan cut out, I just used the armholes as a guide for cutting the sleeves (sorry no picture). Go ahead and cut off all the ribbing too. Since the top seam of the cardigan will still be in use, go ahead and pin the sleeves to the body.
Sew the sleeves onto the body of the cardigan, lifting the pressure foot to relieve tension as needed. Sweaters love to bunch up and stretch on you.
Once the sleeves are attached, use the actual sweater as a guide to cut your ribbing.
Pin all your ribbing in place and attach it. Sew fairly close to the edge.