Good point. Although, she did specifically say it's a single dose treatment and that even a second dose is no guarantee to get rid of all the worms. She said some birds are just more susceptible to heterakis than others, and there's a good chance it's in her genes. So a second dose may not do any good anyway. Poor girl :(
A dose of 50mg/kg (0.23ml per pound) should get rid of them.