Elijah of Buxton

In our Guided Reading group we're reading Elijah of Buxton. In one part of the story, Elijah's neighbor, Mrs.Holten gets a mysterious letter in the mail. When it is read by the main character Elijah, Mrs.Holten finds out that her beloved husband has died. Mrs.Holten escaped from bondadge earlier in life, but Mrs.Holten's husband has stayed in bondadge after getting caught when trying to escape. This mysterious letter is from Mrs.Jacob Pool, and I'm wondering who Mrs.Jacob Pool is. Is she one of Mrs.Holten's friends from back on the plantation or is she Mrs.Holten's old owner, and if it is Mrs.Holten's owner how would she know where Mrs. Holten lived? I guess I just have to read more to find out!
MD