So the issue here is that our cat rescuer saw a momma cat carrying her kids through a very precarious parkour style course, only to leave them in an air con vent. This is obviously a big no no as you have no idea what could come out of that vent and the space they had was absolutely tiny. So to our rescuer's credit the kittens needed saving and she saw that. But once she managed to see where the kittens were and gain access she made her first mistake.
She decided to only take one of the kittens from the litter. Now, we can completely understand that there are very few people who can take on the responsibility of a full family of cats. It is a lot for anyone to handle. But when you see this many cats in need you are obligated to take them all, even if its a temporary measure until you can seek help. Taking one and leaving the rest to their fate is playing a role that us hoomans were never intended to play. But surprisingly the second mistake that this pawrent made was actually worse than the first, but you'll have to scroll on down to find out what it was.