The tendency toward salpingitis and/or internal laying is genetic/hormonal. I've lost six girls to this, but saved Ivy and one of my hatchery Buff Orps, Ginger, who was in the same shape as Ivy this last time. It's not due to dirty conditions--in some high production type birds, like most hatchery RIRs, Barred Rocks, etc, the cloaca becomes "loose" and sucks feces back into the oviduct, causing an ecoli infection. It's not caused by anything external and can't really be prevented. That means that Ivy may do that again in the future, but as she approaches four years old, I think maybe laying less may make her less prone to any reproductive infections. At least, I hope.
I think if she was really laying internally this last time, rather than just having an ovarian infection, that the penicillin wouldn't have done the trick for her. Knowing when to start antibiotics can be tough, since chickens often hide their illness until they are too far gone. I suspect that someone less "hands-on" might just find a dead bird and dispose of it, never realizing what happened. This is probably quite common, really. I just usually see when one of my girls is "off", though not always soon enough to do anything about it, even if I could.