Do you know for a fact there was no food or water in the room? If food and water were provided, the cat should be okay.
The girl has violated a house rule. But I have to tell you, having a cat or two around the place may solve your rat problem.
Many cats will not attack a rat, although they will catch and kill mice. Rats are substantially bigger. However, the smell of cats will often deter a rat from entering an area, which is just as good as killing them.
Something to think about.
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A finger in every pie.