Sasha is Claire's friend, who called Claire to ask if she and Thomas would go out with Sasha and her partner. She talked to Claire shortly before she and Thomas had a fight, and eventually split up.
Claire:"I don't know why drapes represent age for me. I guess it just feels like something my mum would do. Oh, um, Sasha called, they're going out tonight, wanted to know if we'd go. [Thomas doesn't respond] What? I didn't eat all the chips, there's another bag."