Hi there, Carole's find in 1911 does look to be a good fit, unless the lady was fibbing about name, age and POB, as there's only one Mary Louisa Summers born 1870 +/- 5 years in Devon. Maybe she was housekeeper for Henry Morgans. It may be worth looking at newspaper archives to see if there's an advert for this. Ladies used to travel all over the country for this kind of work.
Interestingly, trees on Ancestry suggest that Henry married Ethel Constance Bourner in 1925 Wimbledon, and there's a PR for this marriage which shows him to be 54 yrs old, a widower, and a clerk, which ties in with the 1911 census. The bride was 37 yrs old and a spinster. There's also a child which could be this couple's, Kenneth Thomas LLewellyn Bourner br Q2 1917 Dorchester, no mother's maiden name. The public trees have Kenneth's surname as Morgans, father Henry, but no mother.
The question then, as you say, is what happened to Mary Louisa?