SPOILERS ALERT - why does Mary Anne, in that mental hospital...

... kill herself after that other lady reveals to her that she is a demon? Was she too traumatized by yet another such vision as well as what Milton did to her previously, was she under a demonic spell/possession, did she also perhaps feel too guilty about Kevin's shameful actions as part of being a shady lawyer for a shady law firm or was it something else?

Anyone think they know, thanks.