It was worse than that, it was his memorial, a gathering with the sole purpose of remembering him, reminiscing, celebrating his life, and mourning his death, and she goes there, and tries to socialize, and fit in, and pretend to be just as affected, sad, and confused as everyone else, it's about as diametrically opposite of normal as you can get.
Can you imagine how chilling that would be? You're at a memorial and the person you know killed him just shows up and tries to act normal and sad but also making normal conversation with everyone?