It will also explain why if you don't pursue Monica, she starts asking all the why and what questions, trying to push u towards her. The thing is - idk how good of a friend she is to Monica and for how long they've had this relationship, cause making her go through all that shitstorm just to get the money feels really wrong. But in the horror movies it is usually the least suspicious and most trustworthy character who is the killer. Maybe this is the secret that Monica still has - she knows that thing about Zarah, but she is keeping it away.