I am sorry about your hen. Does she have any other symptoms such as nasal discharge, puffy face, stinky breath, acting depressed? Does her gasping have a gargle or cracking tone to it? If it sounds like it’s coming from her lungs it could be respiratory. I would look down her throat to see if there is anything unusual such as lesions or excess mucus. I read once that gasping can be a sign of parasites (such as gapeworm). Hopefully it’s something minor! I’ve only had experience with respiratory issues in my flock, but I’ve never had an issue with Parasites yet.