Thank you for the info! That really helps.

So I gassed and fed off the 4 others, but unfortunately one of the 2 I kept alive didn't make it through the night. The person I got them from kept them in a tub with the other 5 rats, and between the smelly bedding, being stepped on by its siblings, and lack of ventilation, I think the change in environment/stress was the kicker. Tried to get him healthy again but he was just too worn down

So now I'm left with a single rat who is still pretty young but very sweet. At this point, any other rat she could be introduced to would be older/bigger than her. How long will she be alright without a buddy? Should I be focusing on getting her to another home ASAP or will she be okay for a little while?