Who is Marian Halcombe from The Woman in White and what is their importance?

Marian Halcombe is Laura's half-sister. Like Laura, she is under the guardianship of her uncle, Frederick Fairlie, at Limmeridge House. Marian is fiercely loyal to Laura and very protective. She is described as educated, bluntly honest, practical and kind. Marian is also instrumental in breaking up the romance between Laura and their art tutor, Walter Hartright. After Sir Percival and Laura marry, Marian goes to Blackwater Park to live with them. She becomes trapped there and falls very ill. While Mariam lays ill, Laura is tricked into leaving for London, after which, she is reported deceased. When she travels to the asylum to visit Anne Catherick, Mariam finds Laura alive and falsely imprisoned under Anne's name. She then rescues Laura from the asylum, and and the two women go into hiding. Marian rejoices when Laura and Walter rare finally free to reignite their romance, marry and have a child.