There is certainly this record on Ancestry, but whether it’s your Ellen I can’t say,

Name: Ellen Lloyd
Birth Date: abt 1858
Age: 63
Port of Departure: Durban, South Africa
Arrival Date: 30 May 1921
Port of Arrival: Southampton, England
Ship Name: Walmer Castle
Search Ship Database: Search for the Walmer Castle in the 'Passenger Ships and Images' database
Shipping line: Union-Castle Mail Steamship Company Ltd
Official Number: 114839