Our doggie was recently diagnosed with Ehrlichiosis~ also tick borne and very similar to Lyme, and I believe the treatment is similar.
Sasha has never shown any symptoms~ treatment was 30 days of doxycycline. I didn't want to treat her for it because I didn't want to treat a dog with no symptoms. We were told that if it was a recent infection that the doxy would get rid of it. I suspect she has had it for a long time~ this is the first year they have tested for it as a part of her routine exam. Anyway, my husband really wanted to treat her, so we did.
I think like with Pookie's mom~ you can put it into kind of a remission with the antibiotics.
It's tough because you can't tell if it's normal aging or if they are showing symptoms. Sasha gets Syn-flex (liquid glucosamine & condtroitin) and at almost 12 she has no arthritis or stiffness.
Since the only symptom was the inflamed hip, maybe it's not the Lyme~ active dogs sometimes hurt themselves and since you can test positive and have no symptoms we hope that is the case for your friend.