https://www.backyardchickens.com/articles/safely-administering-oral-medications-to-all-poultry-and-waterfowl.73335/
even though this is for giving medication, it’s an excellent article
Sometimes night checkups are better because the hens are calm when roosting. Grab a headlamp and take your time. even better if you have someone to assist by holding the hen while you look.
Sorry, have you opened her mouth to have a look? It could be something stuck there. A while back one of my hens had this weird sneezing episode, it must have been stuck food or something because it was gone by the next day. It made me nervous too.