It superficial friend’s relationship with Casey. Significantly, she

It is undeniable that Marcia is also a second supporting character of Split. Marcia is a Claire Benoit’ best friend. She has a lot of meaningful moment with Claire, especially Claire’s birthday party. She has a superficial friend’s relationship with Casey. Significantly, she is also one of the teenage kidnapping victims. In the initial scene of Split, she enjoys her life with friends. However, after Kevin kidnaps her, she faces with only stressful and controlled situation. There is no more of her freedom life. Consequently, owing to living initial life without any suffering, it is very difficult for her to efficiently cope with this harsh situation. 
In addition to Claire, Marcia is also the factor leading to abduction. As she is a cheerful and light-headed teenagers who hardly face with abuse like Claire, she made Barry feel pain by pulling his hands under her shirt, resulting in reducing his control over other’s personalities. This situation cause
Barry to feel that Marcia is impure and does not really understand about trauma. Eventually, he follows Marcia and kidnaps her and her friends. 
The thorough consideration towards all information from movie draws up the conclusion that there are three psychological perspectives. Firstly, according to behavioural perspective, she observes the environment in order to escape from the room during the abduction. With an efficient encouragement from Claire, Marcia extremely tries to unlock the door. Secondly, the cognitive perspective occurs when Dennis chooses Marcia to dance, Marcia subsequently follows Casey’s suggestion to pee herself due to an understanding that if she can make herself dirty, Dennis who is a neat person will finally don’t want to get close to her. Lastly, the humanistic perspective can be found when Marcia is reacting to the need for safety and self-fulfilment during the abduction. She naturally strives to leave from an undetermined location. When Patricia brings her out to eat sandwich, she seizes the opportunity to escape but it fails.