She doesn't come immediately. There's an instinct in her that screams fear, so she'd gone to her mother, who she was staying with anyway. There had been a brief but thorough discussion.
Finally, then, Sable arrives -- with her mother. It isn't a gesture of a little girl crying to mommy over bullies on a playground. Sable and Marnie may be mother and daughter, but it has been many years since they became also friends. Marnie accompanies her daughter both as a protective mama-wolf and as a concerned companion. She will not interfere except in the interest of her daughter's safety, but she also has her own personal concerns over the behavior she has witnessed from the boys and will not leave her daughter and friend alone with them, whether or not it is "her" issue to deal with.
Sable enters with her mother, looking apprehensive but calm. Some part of her knows -- or suspects -- what is coming, and she is forcing herself to keep her cool and be rational.