Help! Something is wrong with my Cayuga female

Shes breathing with her mouth open, staying away from the other ducks. She stayed under her house for most of the day yesterday. It's been extremely hot here but she has plenty of water for swimming & drinking. I thought she was choking at first but now I don't think so.

Give her something like watermelon or tomato...Sounds like choke to me? Put it in a deep bowl of water so it dislodges...Probably grass stuck in her throat? Try massaging her neck....It works with mine when they get choke.

Exactly how hot are we talking, temp outside? According to numerous sites I've googled, Cayugas do best around the 70 dg temp area, as temps get higher, they can struggle. Mine is able to handle up to about 100 dg outside with minimal fuss...but that took time. She gradually acclimated to our very intense summer temps (up to 108dg!). Initially, open mouth breathing and fluffing out her feathers, wings slightly positioned away from sides...classic overheating signs. She was much less interested in interacting with her WH "sister", and spent most of her time in the kiddie pool.

If she has something caught in the throat, agreed that offering a treat in a deep water container and/or massaging the throat has worked for my WH in the past....she's a very fast eater and sometimes gets ahead of herself. Though in these instances, whatever was stuck in there moved down in minutes with a little help from me.

If you see other signs of heat stress that I described above: vitamins and electrolytes in her water, frozen ice blocks in most frequented water bowls (I freeze water in cool whip containers), and spraying down areas she hangs out in, midday, are good ways to help her cool. Some suggest frozen 2 liter soda bottles placed in pen though neither of my girls will actually lay near them, but worth a try! Side note: if our kiddie pool, water dishes, or feed station are in even slightly unshaded areas on hot days, my girl won't go near them.

My Cayugas pant when the temps get above 90. I added extra shade to the top of their kennel and I thoroughly wet the pen bedding down each morning when I know it's going to be above 85 (which has been a lot of days recently!) On the hottest days I give them frozen blueberries because that was the only frozen fruit I had for them.

I've placed ice filled 2 liters throughout the run. It's been in the 90s & with the heat index a bit higher. They have several pools for them to play in. She isn't hanging around the other ducks. She stays under the house in the run. She's eating very little. Even though I've offered so many things. I just don't know if it's the heat or something else.

Could be something else, but, honestly, could still just be the heat. Do you see any other symptoms? Have you checked her from bill to feet?

She could be eggbound, panting from the stress. If that's the case, she could use a vet's help. If that is not possible, I would bring her in, put her in a tub of lukewarm water, let her float for an hour or so, and give her a boost of calcium -about 200 mg a day for a few days. You might be able to feel an egg if it is in there, but maybe not, especially if it's a soft one.

Check her vent - any sign of egg white, yolk, or stool that looks like it's mixed with a yellowish curd? Vent tissues at all swollen?
@Asztrid99

And I would also keep her in the dark. If she's eggbound, preventing more eggs from forming can prevent things from getting really rough.