Yes it could be lungworms. Lungworms can be treated with ivomec injectable given orally. I don't know about giving it monthly though. For regular worms you give once, and then again in 10 days and if they have a really bad infestation a 3rd treatment in another 10 days. Once they're wiped out your good to go for a while. Try pulling a fecal sample as well to see if she has other worm issues. But Ivomec will work on most all internal parasites.