OK, chances are she has an upper respiratory infection and/or an allergic reaction. Believe it or not, birds can be allergic to their own feather down and dander, especially during a molt. It's far more prevalent in macaws, but any bird can have this happen.
Let's try this for the next few days while also putting a plan in place to have her seen (I'll go over what the vet should be checking for)
First though, let's keep it simple. As long as this lucky ducky bird is still eating and her droppings are normal and regular, let's clean her cage every day in order to reduce any chance of allergens. This is important because a 'slight' respiratory infection can turn serious in a bird in no time.
If you have a vaporizer put that in her vicinity (no meds in it of course)
The fluffing is her trying to build up heat. Whenever a bird is 'sick' or 'off', they tend to lose body heat. Even in the hot summer this can be a problem that leads to a bigger problem so try to increase her heat. You can layer a doubled over sheet on one side of her cage (use clothespins or other clamps) and then lay a heating pad over that - using the same or similar clamps, but careful to avoid pinching any wires. Ideally put this at the side of the cage where she tends to rest most often. Set the pad on Medium so the heat goes through. You can further cover the whole cage (leaving the front part uncovered) in order to hold this heat in.
You should notice a difference in 24-48 hours. As in no more fluffing up, no more discharge and more activity on her part.
Once we get her squared away, let's talk about those seeds.
Right now though - we're going to do this one little step at a time ok?
Also, if you can put her nearer a window so she gets some sunlight, great! Just be sure that a part of the cage is covered so no matter where the sun is during the day she can escape it to a shady part of the cage. This is pretty important. I had a client who wasn't home to see where the sun came in at all hours of the day; her bird suffered serious exposure complications from being in direct sun/heat and almost didn't make it. I don't want you going through this same thing
Sound like a plan? Of course I'll be with you so check in and let me know what's happening, yes?