I think a lot of people don't understand mental health of mental illness still, it is not a diagnoses to say she is mentally unwell, it's simply factual based on her evidenced behavuour. What is causing it none of us know.
" mental health is the successful performance of mental function, resulting in productive activities, fulfilling relationships with other people, and providing the ability to adapt to change and cope with adversity"
"six major, fundamental categories that can be used to categorize mentally healthy individuals. These include: a positive attitude towards the self, personal growth, integration, autonomy, a true perception of reality, and environmental mastery, which include adaptability and healthy interpersonal relationships"
Amy is clearly not doing this. Mental illness can take many forms, inc anxiety, stress, depression, and can manifest itself in many ways.
Being mentally ill is not an insult. Or a slur. But clearly. Amy's perception of reality is not what it should be. Her view of her relationship with Curtis is a prime example of this. She is unable to cope with adversity. She has integrated the least with the group. Nor is her Ability to form healthy relationships as it should be., she Even struggles with some of the girls, never mind her ability to manage her relationship with Curtis in a healthy non dependent manner.
Most of these in isolation would be irrelevant, but the Curtis thing is hugely telling, believing that they will get married and have children, as is her crying for days after. And then coupling everything else in on top of it.
Call it what you please, not in a good place,mentally unhealthy, emotionally unstable. Whatever you call it. Her behaviour around her relationship with Curtis is far from normal and healthy