Gasping and wheezing can be either gapeworm or a respiratory illness. For the former, use molly's herbals formula #1 at double the dose. For the latter, keep with the garlic and include lots of healthy, easily digestible foods. Also include fermented feed or other ferments such as yogurt for at least one meal/day - for humans, 80% of the immune system is in the gut so I imagine it's the same for animals as well.
A note on molly's: I am right now treating a severe (bright bloody poops) case of coccidiosis in my week-old Cornish x and 2-week-old heritage chicks. Even after just one dose (one tbsp in feed for 37 chicks) ALL were back to normal, healthy poops! I don't know about its effectiveness on gapeworms, but the active compound is delivered through the bloodstream so it will get into those worms as well, but perhaps in lower amounts as compared to intestinal worms.
There are many "weeds" which can treat various other diseases. Dead nettle works on pneumonia and bronchitis, mullein cures mycoplasma... do some researching and see what kind of medicine you have growing in your yard that you can feed to your hen or make tea out of (if she won't eat them).
