Any type of ivermectin can be used to treat lice and mites. I have used it topically, orally, and by injection.
In the US we have:
Pour on for cattle (topically only) - The dose listed above by @Eggcessive is correct.
Injectable for cattle (Can be given by injection, orally)
Oral drench for...
Welcome to BYC. Very strange. If she were mine I would treat for life and mites with permethrin and I would give her a vitamin E capsule a few days in a row as well as some vitamin B complex.
Where do you live?
Since she is limping I am suspicious of Marek's, but do try the vitamin e and b...