If it's respiratory, then you can give her an injection of 1cc of Tylan 200 subcutaneously (under the skin, between the skin and muscle, not into muscle or veins) between her shoulders (NOT her breast muscles!). Don't bother with Tylan 50. I don't recall if Tylan can be water dosed, and if it can I surely don't know the dose per gallon.
It's possible it's not respiratory, and is instead a worm problem, but if her breathing is raspy as opposed to her gaping, then you're probably right. If the Tylan doesn't work or you suspect it may be worms, you can worm her with ivermectin in her water (or sub-q again). I don't know the water dosage, but I want to say it's 3cc/gallon... but if someone else knows hopefully they will speak up. I do all mine sub-q.