She hasn't 'worsened' at all, she's acting just the same as yesterday. she's not droopy and looks 'unsuspecting' physically besides her pale comb and she doesn't seem to have eaten yet.
I have no experience with Blackhead but when i read about it it sounded much worse than what she's showing? We may have some Flagyl here but it's in human dosages... that stuff is Disgusting. I will call and ask the Vet to see if it's something I can get from him rather than buy online.
I have seen blackhead in my turkeys, peafowl and one chicken. They all start off looking "off"... not eating as much, droopy wings, fluffed up, pale. Some have had yellow in their droppings, others had bloody droppings.
Do you have the liquid form or pill form? Doesn't matter, you can make it work either way. Your vet will probably tell you that it's not common in chickens, but the pathologist that I spoke with said that they are seeing more of it in chickens.
Talking to your vet would be best... He can tell you what diseases Flagyl is used for and how to dose them. To treat blackhead, my avian vet told me to give 30mg/kg once a day my mouth for five days and to de-worm with Safeguard .5cc/kg (50mg/kg) once by mouth and repeat in ten days.
When I have treated mine, I usually see improvement in 2-3 days, if I have started treatment in time. The ones that I didn't treat soon enough also developed secondary systemic bacterial and fungal infections