She argued to Will it came from childhood trauma, but when he pressed her she described traits of herself from before the event that were signs of OCD. Saying that she was very anxious as a small child and a very fussy baby. Not that that's the same as OCD, but high anxiety in children can develope into OCD in adults. So, theoretically, she may have been "born that way," and deteriorated into what we see today over time.