step is to look at the consequences of each person's actions.
The roommate is almost certainly in favor of strict social distancing because she doesn't want to get sick herself. Human nature, and nothing wrong with that. But her insistence on following strict social distancing *benefits* everyone in both households, in that their risk of getting infected with COVID-19 is decreased.
Meanwhile, the girl who doesn't want to comply with social distancing is increasing the risk of everyone around her.
Now, you tell me who is right and who is wrong in this scenario? The answer is fairly obvious.