As Ellie May said: Ivermectin does not kill adult heartworms. The injection you are referring to, I am quite sure, is Immiticide.
Here is a link that explains heartworm treatment clearly:
Heartworm Treatment
I have never heard of weekly treatments for heartworms...and I have never heard of treatments being spread out over an entire year.
I don't see how the protocol could be any different in any country. I think you really need to ask your vet for more details about what protocol he is following. Her bloodwork would have nothing to do with heartworm treatment unless it was altered from the beginning in which case she would be considered high risk for treatment with Immiticide.