Help! Huge respiratory issue with adult hens and we have baby chicks too!

Please help. I don't know what to do. I have a feeling someone will tell me I have to cull the entire flocks, but Im not willing to go there. We have a flock of 7 hens outside, about 2 years old. One of the RLB wyandottes started sneezing, and she's been flicking her head. Last night she did a woodpecker thing against the wall when I locked their coop and there was blood all over her beak (I actually can't remember if that was this morning or a day ago). She had splattered blood all over the wall too. Anyway, she was acting fine today other than the sneezing but there had been a clicking noise too, and tonight when I went to lock their coop, I noticed a couple of pine shavings by the chicken door had blood on them (just cleaned the coop today so I know it's fresh), and when I opened the people door I noticed her mouth was full of white mucus! To make matters worse, I have 13 4 week old chicks and 5 2 week old chicks in the house. To make matters even worse again, I peaked in on the chicks this afternoon after I had been out cleaning the coop, and one of the baby babies looked like it had blood on its wing, so I reached in and grabbed her. Turns out another chick had pooped on her, so it was dried poop, but I hadn't washed my hands, and hadn't changed clothes, so now I'm even more afraid of biosecurity issues. Back to the sick one though, I have Denagard. I don't know if I should have, but I mixed some up with water and went back out and forced her to drink a few swallows of it. I don't even know if that will help, but I panicked. What do I do??? I'm freaking out just a little at this point. Please help!!!

So after doing a bunch of research, I'm worried it might be ILT. There were blood spatterings on the coop wall at head height, there is mucus in her mouth,open breathing, clicking when she breaths, and she has bloody looking nostrils. The only thing that doesn't seem to match is she has no facial swelling and no eye issues. The main symptom that makes me think it is ILT is the blood spattering though. After reading someone's page here on respiratory diseases she states that you usually know its ILT when you find the blood spatterings at head level.
Other than culling, is there anything I can do? I don't understand how she got infected. We have not been to any farms or with any people who have chickens. We have "coop shoes". The only thing I can think of is mold spores in long grass around the coop. I read somewhere that it could be a problem, so I made sure my husband weed whacked around their run. We did order baby chicks a month ago from two hatcheries, but im guessing they didnt bring anything with them. Im really worried about the baby cicks now too! Any help would be greatly appreciated!

Isn't there anyone who can help? Can I use oxine to mist their coop and run and their faces while I am treating them with denagard? I now have two with clicking noises when they breath.

Thanks Seminolewind. I haven't had new chickens (except the baby chicks inside) for 2 years. Im not sure how they got what they got it unless it came from the wildlife around here. We have a cow farm behind us, and wooded area as well. I will, however, say that in my more ignorant days in the beginning, I mixed ages. I had originally gotten my flock of 11 from a farmer friend. A couple ended up being cockerels so we would take them back and swap them out for pullets, we lost one in the very beginning due to a genetic issue (I know that because we took it to an avian specialist and it cost us a pretty penny to walk away with a euthanized chicken), rehomed a polish crested special needs chick to a home she wouldn't get picked on at, and then the last time we had a rooster, the farmer decided to give us two hens from her two different flocks that were older so we would know for sure they were hens. We have lost 3 over the last year and a half (last one being a year ago). One of the older ones never got over her worm load no matter how hard I tried, one was unknown causes, just lost energy, secreted clear fowl smelling fluid from her vent when I brought her not the house to nurse her, and the other was a polish crested that we realized had blood sucking lice in her pompom too late. The one wo died of worms I believe was the cause of the lice and worms for all. She had them both first. I will never mix ages again because I believe that is when my troubles started. There was a time last winter when my other Wyandotte had a gurgle in her breathing, and they have all sneezed on occasion, but Ive never had the mucus in the mouth or anything so severe as this. The one who I was worried about last night was mucus free this morning and walking around just fine like she has through this whole ordeal, but I'm afraid our black Cochin now has the clicking noise too, and a few of them sneeze. I made the Wyandotte drink the Denagard water last night, and I have Denagard in their water today, but I've noticed the Cochin has retreated to the coop. These are my pets. I'm vegan! I really don't want to lose any of them or cull them. I make sure nobody goes in the run without coop shoes, and we rarely have our friends near them. My older son's teacher wants us to bring in a baby chick, but I'm going to say no because I'm afraid of the biosecurity issue. Ugh! We were having such a good stretch of time with healthy (acting at least) birds. I don't understand how my farmer friend can be disease free. She has 2 different age coops and fenced in areas in the field right next to each other. She never has biosecurity issues. She orders baby chicks each year too.

Update! Knock on wood everyone is doing well. After the one night where there was white mucus in my hen's mouth and I forced her to drink some water with Denagard in it, we have been mucus free. I have them on the Denagard solution, and no more clicking noises when breathing either. I know some people don't agree with keeping chickens once they've had respiratory issues, but we plan to keep our chickens until they die of old age (hopefully not disease), and will wont be ordering anymore baby chicks.