Based on the pics and my experience, "she" looks more like a drake to me - especially in the most recent pic of her next to the lighter duck in the weed bin. She/he reminds me of two drakes I had, except they had about as much caruncling as she does by the time they were 6 or 7 mos old. They had curvier bills, thinner legs, smaller feet, v-shaped tails, shorter bodies, shorter mohawks, were fairly small (5-6 lbs), and they tended to step on their feet as they walked - all signs (I had read) that they were ladies. Eventually they only hissed and huffed, and once mother nature told them to go sow their wild oats it became pretty clear that we had drakes on our hands.
Different lines vary in size and amount of caruncling, but your new one does look much larger than your smaller brown duck in the plastic bin. Did you get a chance to see any of the brothers or sisters that hatched out with the one you were given? It's a lot easier to tell if you can see them next to a duck or drake from the same clutch. The drakes will be obviously larger than the ducks.
I would say keep an eye on him/her and listen for vocalizations. Since he/she is a year and a half it's not quite the waiting game as when you're dealing with a duckling. If you hear anything other than a hiss, or she lays an egg, you've got yourself a duck! Otherwise, you have an unfortunately tricky situation on your hands. Ending up with surprise drakes was how my flock grew this last time.
