What illness did Vanessa's mother suffer from in the novel, The Wife Between Us?

It is known that Vanessa’s mother suffered a mental illness that caused her to have days she was so depressed she was unable to get out of bed. Vanessa often wonders if she inherited some of her traits of obsessive thinking from her mother. Knowing the status of Vanessa’s mother, Richard sometimes accused Vanessa of being crazy, like her mother.