Chicken excessively yawning, shaking head and throwing food around.

[georgeg78]

She may have ear canker, hard to know, but hopefully your vet can figure it out.

The stretching of the neck reminds me of a bird trying to clear the crop, it may be sour/fungal infection and/or canker (trichomanias). I wonder if she's got a blockage.

Your vet can do a fecal float to determine if she has worms/check for Gapeworm. Ivermectin is not usually the treatment of choice for Gapeworm here in the U.S., it's not that effective. However, the Flubenvet should treat Gapeworm if given correctly for treating Gapeworm - I believe it is supposed to be given as 3 doses 1 week apart for treating Gapeworm, but ask your vet, it should be in their formulary.
Panacur (Fenbendazole) and Albendazole are both good to use for Gapeworm.

As for using NuStock in the ears, I'm not certain about that. If they are gunky, then if she were mine, I'd use 1 drop of Peroxide in the ear, let it bubble up, wipe clean. Repeat once more if necessary. A thin layer of triple antibiotic ointment can be applied in the ear.

Does she have any mites or lice?

Thank you!! No she doesn’t have mites or lice. I asked my vet about peroxide and he said he wouldn’t risk it, but I’ve seen it suggested a few times here and just wondering if he’s being a typically reserved British vet (!) I do have some hydrogen peroxide so could do it, just nervous

I really appreciate your response here (and others), it’s kept me a little saner in trying to help her!