To me psychological thrillers are chilling in their small realistic details.
Quote:
She has a well paying office job
Her career, as stated, is unrealistic and flat. There are no well paying office jobs. There are well paying jobs done in offices, but they're referred to as professional titles; accountant, engineer, etc. (Anyone who has established a professional career has outgrown
childlike and
insecure.) And frankly, the workplace simply doesn't reward
childlike and
insecure with a living wage unless there are extenuating circumstances such as; a relative owns the company.
I am assuming that the plot requires her to have some expendable income in addition to being financially independent. Has she inherited money? Or has she been wreaking havoc in a business she inherited and runs?
Or give her a job or special interest that has some skills/assets that can be put to chilling use; it's especially chilling if the job is mundane and the skills/assets are used in very unexpected ways. (I'd avoid computer hacking because this has been written to death already.)
She will need a back-story which explains how she arrived to her 40s still childlike, etc, but has expendable income. The back-story needn't be spelled out in detail, it can be presented in broad brush strokes but it needs to be plausible, congruent with her immaturity and explain her financial independence. Fleshing out this area of the character's life may also yield a lot of plot movement