OK so Tracy, is your duck broody? the only thing she needs is access to WATER, as long as she can get into some water she will COOL herself down. I understand she's blind but again, Even though she is I'm sure she's still able to find food and water. If that's the case, she's all good.
As far as being cold, I doubt it. They can tolerate cold weather, all heat is processed through there feet. The feet makes all the necessary adjustments. So I wouldn't worry about a fan, I wouldn't worry about a heating lamp, I wouldn't worry about anything but making sure she has water.... and food. Let her be a mommy, she's GOT THIS..