She's addicted to porn.

"It's kind of a personal problem. You won't tell anybody, right?"

"Everything you say here is completely confidential, yes. Nobody outside this room will ever know what you tell me, and I will never judge you."

"I think I might be, um, obsessed with porn?"

"Watching it, or making it?" Wendy asked, and noticed that Phoebe's thighs squeezed together slightly.

"Watching it. Recently I've been doing it all the time when I can."

"When you're alone in your house?"

"Oh, that's the best... I can just play the sound through the speakers and nobody will hear." She seemed to be imagining it as she spoke, a look of fondness passing over her. "-but," she remembered that she was supposed to be trying to stop, "Even if I'm not alone, I'll just put on headphones."

"Do you masturbate while you watch?"

"Sometimes. Sometimes I can't because there's somebody else in the room, and sometimes I'm just not in the mood."

"So even when you aren't in the mood to masturbate, you're still in the mood to watch porn?"

"Oh, it sounds so perverted when you put it that way... but I suppose so."

"Do you ever watch porn outside of your house?"

"Yes. It wasn't all at once though. At first it was just me alone in the house wearing headphones. Then I took off the headphones, and then I started doing it while other people were in the house. Then I started doing it in the backyard every now and then. Then I let myself watch while somebody was in the room with me. Then I tried the front porch."

Wendy thought it was interesting that she went outside before doing it with somebody in the room with her. "Was that the end?"

"No. One day I was in a bathroom at the mall, and I got the urge to do it, and I have a smart phone, so I just... After that I guess I realized I could use my phone for it, so I wanted it more in public. I would duck into a bathroom, but eventually I'd just find a quiet corner and put in my earbuds. If I couldn't put in my earbuds, I'd look at pictures, and if I couldn't stare at my phone, I'd listen to audios. I could do it basically all the time after that."

"Hmm..." Wendy thought for a moment. "I think I have an idea."