Questions about the ending **********Spoilers*** ***

I would love to know what Courtney's (the tenant) "plan" was at the ending! First of all the wife's best friend is dead in the pool. Secondly, Mrs. Vegas is dead in Courtney's bathroom.. Thirdly, the wife is drugged and has her mouth covered in duct tape in Coourtney's apartment and fourthly, she calls the police about a domestic disturbance before the husband has even arrived home! Then she starts shooting at the husband outside.....I mean what exactly was her PLAN??????????????????????