I am a manic "pre-washer"....mainly because I use lots of vintage and op-shop purchased fabric and wools. I even prewash new fabric, just to test shrinkage, colourfastness and to remove any chemicals from the dyeing process.
I agree with Butterflywing, do a test piece first, that way you will avoid disaster. Maybe you could back it with a really light-weight woollen blanket? Anyway, I think it sounds a wonderful project and it would be nice to see it when it is finished. I am sure the recipient will find lots of comfort in it.