Who is Teddy Eleanor Reeves from Sybil and what is their importance?

Teddy Eleanor Reeves is Sybil's roommate in New York City. She only pays a minor role in the novel, but Sybil refers to her several times and notes that Teddy sees that Sybil is different and supports her treatment. Teddy is also able to differentiate between Sybil's more prominent selves.