Answer:
Nina is most likely in the precontemplation stage.
Explanation:
An individual tends to go through a series of stages in order to make a change and stick to it. The model is round, which means that change is rarely lineal and it is possible to go back to a previous stage or star over, for example.
The Precontemplation stage is the first one; it occurs when an individual has not yet identified a problem or does not yet think he/she needs to make a change.
Nina dismisses her brother's comment by saying she does not have a disorder so she is in this first stage.