Washing crochet blanket.

I've made my Mil a huge crochet blanket in red, white, and black, her birthdays tomorrow and I'm giving it to her then but I'm not sure what to tell her about washing it (she's thick and can barely wash a sock). I'm worried about the colours running and ruining it, I've lost the instructions from the wool I used so I'm looking to see what all you artistic people say, tia x