Chances are it wasnt contagious. Its not worth getting all worked up over. Just get some poo and take those other guys in for a check up soon to be on the safe side.
You hear horror stories of people losing entire collections due to one sick snake but how many people has that actually happened to? Very very few. More often its mites that infest entire collections.
Alot of illness can go un noticed for a very long time. RI can go on for many months or more if the snake has a strong immune system and the husbandry is correct.
Just dont get get too worried about the others just yet. They are probably fine. They are eating and breeding. If they are nice & thick, breathing fine, clear nostrils, shedding fine, clean pink mouth, then I bet everyone else is ok. That girl must have had something for a long time. Snakes are like birds that way. It takes a trained eye to notice any illness. They hide it well.