More research has established the identity of Mary White who is mentioned in the family correspondence of 1955. She appeared sometimes to be a sister to the Penny children but is never listed among them in census returns. Her history is as follows:
Mary Jane Rowland, born 17 March 1880 Yeovil district, subdistrict Ilchester at Bridgehampton, apparently illegitimate daughter of Jessie Rowland, born Upottery, Devon (1859-1936). No father's name is given on her birth certificate and she keeps the name Rowland until her marriage to James White. At time of Mary's marriage to James White (1873- of Knole, Somerset) in Dorchester in 1902 (Dorchester Mar 1902, 5a 579) she gave her name as Mary Jane A. Rowland.
She lived with her grandparents until of age rather than live with her mother who marries a year or so after Mary's birth. Her mother, Jessie Rowland, marries Henry Penny (1853-1905) in abt July 1881 (Sept 1881, Yeovil 5c 637).
The 1911 census shows Mary living in Weymouth with her husband and two children: Fred White born 1906 in Avon, Hants. and Ivy May White born 1903 in Rampisham, Dorset. Mary was still living in 1955 (family knowledge).
So what is Mary's connection with the Penny family siblings described in this lookup request? She is actually a half-sister to them. Two pieces of evidence identify her as being regarded as 'sister' to the Penny siblings. The newspaper obituary notice of Lucy Ann Penny (1882-1955) describes Mary as her 'sister'. Also the 1911 census for Mary and James White in Weymouth shows Ernest Penny (1892-WW1) living at that the same address and is described as 'wife's brother'.
Mary Rowland as a child/young woman;
1881 census: living with mother Jessie Rowland at the home of Jessie's parents (John & Elizabeth Rowland) in Downhead, West Camel, age 6 months?
1891 census: living with grandparents, age 11, John & Elizabeth Rowland at Bridgehampton. Jessie now married to Henry Penny, living at Church Hill, Corton Denham.
1901 census: living with grandparents, age 20, John & Elizabeth Rowland at Bridgehampton. James White, her husband shortly to be, listed as a boarder (age 27, a carter), born Long Sutton (close to Knole).
QED