SHAHB -- I don't have AASHTO in front of me for a reference, but you should ignore the wind force for the entire area above the mid-height of the girder (for local bracing design/effects). Wind on the parapet carries to the deck (which is a wonderful diaphragm for lateral loads). Wind on the top half of the girder carries to the top flange (typically continuously braced and not controlling the design) then to the deck. I think it's in the earlier parts of 6.10 (mabybe commentary).
Saying that, I would consider the wind force acting on the area of half the girder height times the brace spacing, and apply that to the bottom node. Assuming typical bridge dimensions and without any other information on member sizes, I'd assume that the x-brace diagonals are an order of magnitude stiffer in tension than they are in compression. So I'd carry 90-100% of the force in the bottom chord (C) and tension diagonal.
If this is from the SE exam, that test is known to gauge your ability to discard irrelevant information and boil the problem down to the necessary parts. Sounds like they might have caught you on this one.
If this is from the SE exam, you are also in violation of your agreement not to discuss specific material from the test. Just FYI.
----
The name is a long story -- just call me Lo.