Sarah didn’t say the word contraception but at end of chapter 20 when Sarah and Dan were conversing about the aftermath of Lester entering the home and his wife. They talked about Lester’s breeding kink
“It’s just some dumb thing Lester wanted. Something about him not being able to do it now and wanting to live out the experience. It’s just sex talk, Dan. It’s not real, you know that. He’s fixed, and besides, I’m not an idiot, okay? I’m not just going to have sex with someone and not take precautions.” Sarah added.
“I hope it was good,” Dan said. He wanted to dig more into the precautions she mentioned but wanted to jab at her first, “Did you enjoy yourself?”
Also we assume she was picking up birth control prescription in pharmacy section of Costco when she went to pick up dinner for Dan