Just to add, it isn't odd for a bird to flap before it dies. Not too uncommon for some of the components of their crop to come up either. You did a really good job considering everything! ❤️
Are you sure they are mites and not lice?
Mites/lice are nasty little creatures. I would try to get some Permethrin dust ASAP. As for the DE, I have heard that it may work for a few days, but the infestation comes back. Mites and lice affect adult birds as well and she is just a chick...
Maybe she was a late hatch. Broody hens abandon the nest if some of the chicks have already hatched and need to eat and drink.
Do you know what brand and size you are feeding? Chicken feed can come in pellets, crumble, and mash. Chicks like crumble or mash.
If he still says no, I would try to find a glass jar and fill it with some warm water. If she stays next to that, it can give her a tiny bit of heat at the very least.
You are doing great. I totally understand!! My dad can be like that sometimes too! Which to me, also makes a bit of sense. But when I grow up, I will be able to do what I want.
Anyhow, this might be your sign to get a few chickens! They are amazing birds! I wish you best of luck and I hope...
Do you have sugar? Sugar water could be good too. I have never used nor do I know what raw agave syrup is, so I do not want to lead you into the wrong direction.
I use a heat lamp.
Your friend gave you DE. Diatomaceous Earth. It doesn't work well with infestations and it becomes useless once wet. Permethrin dust works best, but I am not super sure if that can be used on chicks, I would assume so though. Maybe someone could hop in and talk about that more.
She doesn't look...