She probably is a restricted Mallard, but without the light dilution of the Silver Appleyard. A key piece of information is what she looked like as a duckling. If she is restricted Mallard, she would have looked almost identical to a normal Mallard duckling. If she was Appleyard, she would have been yellow with a dark stripe on top of the head (some birds sold as Appleyard are not really). If she was WH, she would have been yellow with a darker dusting to the feathers, but no stripe on the head.
I don't think she is a WH. Her coloring and size is not right for WH (and definitely not a Gold WH, as Golds virtually never would have a blue wing speculum). Snowy Mallards though are almost the same genotype as the WH. The WH just has the addition of Dusky (and the Golds also have brown dilution).
My vote is restricted Mallard, but could also have something else as well. I would love to know what hatchery she came from!