"[Ali's] mom actually has some dark secrets of her own, which end up tying in to Ali," Sasha Pieterse told Us Weekly in their special Pretty Little Liars edition, which hit newsstands in July.
Like mother, like daughter, we know Mrs. DiLuarentis has trouble controlling her temper — case in point when she nearly took Ali's finger off when she slammed the piano lid on her fingers — so perhaps she lost her cool one evening with Ali, and now she's doing everything in her power to make sure no one ever figures it out. After all, we’ve seen Mrs. DiLaurentis exhibit mean girl behavior in the snipes she makes about Hanna’s weight.
Not to mention, whoever Red Coat is, she has a serious compendium of knowledge about Ali — especially her relationship with the Liars. Plus, it's not like she was in any hurry to find out who was sleeping in her basement's crawl space. In fact, she didn't even want to report it!
What do you think, PLL fans? What is Mrs. DiLaurentis hiding?