Are you sure it's gapeworm? You said that she's been wormed already, and the symptoms often mimic that of pneumonia, and gapeworm in and of itself can often lead to pneumonia as a secondary infection. If you're still giving her the tylan I'm not sure I would continue. She either needs heavier prescribed antibiotics or flubendazole, or even both together.
Safeguard given several days in a row treats gapeworms.