Historically, artistic people have been regarded as social recluses. Maybe, talent manifests because of this lack of interaction and they have a need to express themselves, or are talented in spite of being outcasts, but whatever.
“Mona” is clearly very creative, and, as she had no outlet for her ideas in the real world, decided to utilize it in creating something in the imaginary world.
I can sympathize with this. I, too, am an artistically inclined person. However, while I have never had much trouble communicating with other people, I understand her need for a friend who she can control, and make sure does not leave her.
So, in reply to your initial question, I do think that being rejected could lead to her delusions and her bluntness, because she has been separate from society and the rules it would otherwise have imposed on her.