My lab killed two of my roommates rats?

she apparently rammed her body into their cage and killed them...she didnt eat them or rip them apart, just broke their necks. is this normal?? i feel really awful about it because my roommate was really upset naturally, but should i punish my dog or is this just a natural behaviour?
Update: they were pet rats...i don't understand why she has pet rats but still. i feel bad this happened
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