First, take a look at the sweaters to see what she wants you to work with.
My mom sewed together chunks of knits with a zigzag stitch so it ended up being more like a knitted afghan than a quilt made of woven fabric.
if the stretchiness of the knits are approximately the same, i would draw squares or rectangles on the fabric, then stay stitch on or inside the lines to prevent " un - knitting" - and then cut the pieces out. I would then overlap the pieces by 3/8 to 1/2 inch and use a multistage zigzag or serpentine stitch on the edges. Sew two seams.