What does Theresa Mo mean by her actions and the message she sent. Why would she think so unhealthy about them?

Rosa's mother became sobered. Has she done something that makes Theresa feel uncomfortable? Or had she said anything that made her feel unwelcome?

For the rest of that day, Rosa, her mother and brother were unhappy. They never expected that things would end this way or that Theresa would one day leave them without a genuine reason for doing ...