Considering rescue dog with Heartworms..seeking input

We are considering the adoption of an 18 month old Catahoula rescue with heartworms. She is very calm and mellow (don't know if this is from the heartworms, medication, recently being neutuered, or just her happy persona)

Regarding the heartworms - we were told it's a light case. We know she's being treated with doxycycline and heartguard. We were notified the preferred treatment isn't available.

Should we have any concerns regarding this dogs longterm health? Will the doxycycline alone be able to kill off the worms before they can do damage to her heart/lungs? Not knowing a lot about heartworms and the mediciations, we are asking for your advice and experience(s).

Thanks for your input

No personal experiences but this looks like an excellent site to get info from ...
http://www.heartwormsociety.org

Thanks murf!