Who is Mrs. Lorrimer from Cards on the Table and what is their importance?

Mrs. Lorrimer is an attractive, well spoken, ladylike woman in her sixties. She is also one of Mr. Shaitana's suspects. Lorrimer admits to killing her husband many years before without hesitation, and rather than worry about it, she takes Anne Meredith under her wing. In the end, Miss Lorrimer is murdered by Dr. Roberts.