The way Alex shrugs tells Hopper everything he needs to know about her feelings on the subject of her mother. He doesn't say anything else, he doesn't need to piss her off or hurt her over a woman who isn't even here.

He'd rather she keep feeling that she can talk to him when she needs to.

"Because you didn't like it or because you liked it too much?" he asks with a faint smile he knows she'll understand.