Noirin is trying to make the guys in the house fight over her she is totally self obessed.
She is trying to make out to Siavash and Tom she is the innocent one in this and Marcus is after her big time. Yes Marcus fancies her but she let him believe he had a chance with her and now that Tom is in the house she is trying to distance herself from Marcus to get in bed with Tom.
She told Marcus that Tom had called him her bodyguard even though she is the one who indirectly made out to Siavash and Tom that if anyone fancies her Marcus is the one they need to watch out for, why would she do this? she wants the guys in the house to fight over her