A little worried

To say I am a little worried is an understatement really, I am very worried about Hummingbird our grey cria who is about 9 months old.  She was weaned three months ago and had been reintroduced to the herd with no problems until two weeks ago we weaned the rest of last years cria and decided to put Hummingbird with the rest of her piers, this would make halter training easier as all the weanlings would be in one place.
A few days ago we noticed Hummingbird was looking a bit lethargic and wasn't eating, every time we went to their paddock she was sitting down, not interested in anything.
Ok what could it be the rest of the group were all as bright as buttons, Worms?  gave here a dose of Zolvic, she picked at her food the next day but really wasn't any better, she had a dose of Vecoxen and we gave her a mineral drench.  still no improvement but no worst either. I was afraid she was becoming dehydrated so gave her a syringe of water a couple of times a day.  By now I was becoming a bit desperate so we thought we would try some Cows Colostrum just in case it would help.  After a couple of days and no improvement I wasn't sure what else to do next.  Last resort I tried some honey rubbed inside her mouth, well don't know if it was a coincidence but she was up and went straight to the hay bag, started nibbling.  There hasn't been much improvement since but I am going to continue with the Colostrum for a couple more days and she had another dose of honey today, she seems to be a bit brighter but who knows!

Why do we put our selves through all this?