Kathy,
I sense by your last post that you have realized that this 1000lb animal isn't going to just stand there and let you mess with her. I wasn't going to step on the toes of others while I gave you my advice.
First choice, like Alice and I said before, get her to a vet or have one out. I think, while LA200 may help, it is the wrong antibiotic of choice. LA200 is for things such as pnumona (sp), snots, pink eye, not neccassily infections. Penicillin is my drug of choice for infection and like LA200 you only have to treat her every 3 days (long acting pen). Just my opinion.
second if you still want to try it yourself, hopfully you have a panel or a gate you can take off and use as a panel and pinch the cow between a strong wall and the panel or gate, tie it very secure, with the bad foot toward you. You should be able to treat her safely then.
Good luck,
Alan