VetRx won’t hurt, and some people swear that it helps. It has only herbal oils (oregano, rosemary, and pine balsam) and camphor, so there isn’t anything strong in it. Vicks salve might do the same.
Have you ever experienced a respiratory disease in your flock? Most can make carriers of the flock and you would probably see the occasional outbreak. You could look inside her beak for any mucus or yellow material inside. Gasping is kind of hard to narrow down. If you see any bubbles in an eye, I would start some antibiotics in her water. Tylosin, doxycycline, or a combo can treat mycoplasma.