Oh gosh, I often napped on the couch when my little ones still woke through the night. I can't see the harm, as long as you know that you sleep lightly so you will hear your GD when she rouses.
You and GD can have a quiet hour together. Depending on her age, if she naps in a cot, then nap next to her on the sofa . If she naps in a bed, then lay down with her, or put a baby fence across the door so she cannot wander.
Obviously I am a lover of naps!