Detectives: MRS. MALORY by Hazel Holt

A complete list to date of mysteries starring amateur detective Mrs. Sheila Malory, a "no-nonsense English matron with a penchant for marmalade, nineteenth-century novels, and snooping." Written by Hazel Holt:

Mrs. Malory Investigates (Gone Away) (1989)
The Cruelest Month (1991)
The Shortest Journey (1992)
Mrs. Malory and the Festival Murder (An Uncertain Death) (1993)
Mrs. Malory: Detective in Residence (Murder on Campus) (1994)
Mrs. Malory Wonders Why (aka Superfluous Death) (1995)
Mrs. Malory: Death of a Dean (1996)
Mrs. Malory and the Only Good Lawyer (1997)
Mrs. Malory: Death Among Friends (Dead and Buried) (1998)
Mrs. Malory and the Fatal Legacy (1999)
Mrs. Malory and the Lilies that Fester (2000)
And the Dying is Easy (short story "Journey's End") (2001)
Mrs. Malory and the Delay of Execution (2001)
Mrs. Malory and Death By Water (aka Leonora) (2002)
Mrs. Malory and Death in Practice (2003)
Mrs. Malory and the Silent Killer (2004)
Mrs. Malory and No Cure for Death (2005)
Mrs. Malory and a Death in the Family (2006)
Mrs. Malory: A Time to Die (2008)
Mrs. Malory and Any Man's Death (2009)

More detectives:
MISS SILVER by Patricia Wentworth
ALBERT CAMPION by Margery Allingham
AGATHA RAISIN by MC Beaton 
MRS. JEFFRIES by Emily Brightwell
SISTER JANE ARNOLD by Rita Mae Brown
100 Mystery Series: 1887-2010
Retirement is Murder: 10 Senior Sleuths