Since I didn't have any sort of nightgown pattern, I used Simplicity 9513 View E, lengthened to 56 1/2 inches and with modifications.
The last time we visited my bf's sweet mother, she asked if I would mend her favorite dressing gown. She said it's her favorite gown, as she likes to be warm and cozy drinking her coffee in the morning. So I took her existing gown home (the red one below) to mend, and then had a template for her exact sizing.
I copied the sizing and the styling of her fav, with a standup collar, side seam pockets, a front zip that stopped 7 inches below the front neckline, adding a ribbon tie at the neck. I used a leopard print polar fleece.
It's long and warm and cozy.
I hope she likes it.