Icatty, sorry you are going through this. I have lost chicks, too, and after reading more, it may have been Marek's, but I don't know for sure. I lost one chick in each of two hatches; none of their hatchmates became ill. However, you can give the rest of your birds that may have been exposed a dose of the Hypericum 30C. If they have it, but haven't displayed symptoms yet, it will help. If they don't have it, it won't hurt. Only give it once. More is not better when it comes to homeopathy. I don't know enough about chicken anatomy to say it doesn't have to touch the nasal passages. It does need to touch soft tissues where it can be absorbed. In humans, the pellets are placed under the tongue and allowed to disolve for best results. When given in water, it is usually held in the mouth for 30 seconds or so before swallowing. With our pets, I just toss some pellets in their mouth and they swallow them - it still works.
If you are seeing improvement,
do not give any more.
Only re-dose
if the improvement stops or
if after giving it some time to work, she starts getting worse. You do not need to jump to 200C if you do not have it on hand. To slightly increase the potency of the 30C, put 1-2 pellets in 8oz. of chemical-free water in a clean bottle. I use a 16 oz. bottle of water and pour out half. Let sit for 15 minutes to let the pellet dissolve. Then succuss the bottle by firmly hitting against your hand or other firm surface 10 times (make sure the cap is on!) Give her a dose. Each time you need to give her a dose, succuss the bottle 10x before you give it. Again, do not give her a dose if you are seeing improvemnt - just give it time to work.
If you do decide to get the 200C, be cautious about re-dosing as you are more likely to cause an aggravation with the higher potencies. You may want to do some reading on using homeopathic remedies if you have not used them before.
Homeopathy: An A to Z Home Handbook by Alan Schmukler is a good book. It is available for Kindle, which can be downloaded to your computer (as can the Kindle for PC app to read it, which is free). There are others, but this is a pretty easy read and I like his attitude.
I know this all sounds crazy, but it does work if you have the correct remedy. I am not an expert, but I do use homeopathy regularly at home with my family and our pets. PM me if you have questions and I will do my best to answer them.
I hope this helps and good luck!