"Sarah!" The exclamation was immediate, and she was positively beaming as her pace quickening to return the embrace. Cathy had been looking forward long before, even when she had thought the other people involved were strangers to her, let alone one of her very best friends.
She gave a confirming nod in response to the other woman's words, responding in a dropped tone, "I had no idea you knew each other." In her delighted surprise, she failed to notice the way Sarah was looking at Lindsey; in contrast, she was thrilled. The complexity of the situation--of the relationship between the men--had been omitted with the invitation, and thus she was more than a little out-of-the-loop.
Finally breaking away from Sarah, she turned to Peter, extending her hand and giving him a friendly smile as she introduced herself. "I'm Cathy. It's so good to meet you!"