Who is Reverend Mother Tamalane from Chapterhouse: Dune and what is their importance?

Reverend Mother Tamalane is is aged, wrinkled, and amused at the thought of Reverend Mother Superior Darwi Odrade giving birth to her own father via the Sisterhood's first axlotl tank, "Tam" is too old to be anxious about the Honored Matres threat. She makes ludicrously sparse suggestions and is pulling back from life. Odrade keeps her for her shrewdness and famous intelligence until Sheeana is ready to take her chair on the Council. Tam remains as a valued advisor, Shares memories with Sheeana and accepts her as her sister - becoming a Janus pair - and accompanies Odrade on the suicidal mission to Junction to face the Grand Honored Matre. Tam perishes at the onset of battle.