One of the basics of introducing cats to a household is keeping them separated - in a separate room - from the other cats for a week or two or longer, depending on how introductions go. I kept both Ginger and Mojo in our smallish computer room (at separate times) for a couple weeks each. They were better than fine.
When a cats world is turned upside down by being brought into a new territory, they find it comforting to be in a small area. That way they can get to know the space, and make it smell familiar with their own scents. This is far from cruel, it's actually less stressful for the cats. Besides, you mentioned that she has a bunk bed - that means the cats have twice the amount of space that people to, since they make full use of vertical space.
Granted, the space where she's keeping them should be clean, and cat proofed, but there aren't a whole lot of people who would open their home up to someone else's pets to petsit. And, it is only for a week. If this were a permanent situation it would be different. But it's not.
When a cats world is turned upside down by being brought into a new territory, they find it comforting to be in a small area. That way they can get to know the space, and make it smell familiar with their own scents. This is far from cruel, it's actually less stressful for the cats. Besides, you mentioned that she has a bunk bed - that means the cats have twice the amount of space that people to, since they make full use of vertical space.
Granted, the space where she's keeping them should be clean, and cat proofed, but there aren't a whole lot of people who would open their home up to someone else's pets to petsit. And, it is only for a week. If this were a permanent situation it would be different. But it's not.