I realise you might have information that we don't but the only way to go forward and try to find Lizzie is by exploring every avenue we can think of. Sometimes the obituaries can help us with a time frame and show if other siblings are still living at that time. We might find that Lizzie also followed John and immigrated to the USA - its just finding those tiny links. John Casey passed away Burbank Los Angeles California - might try an e-mail to
http://burbanklibrary.com/I did notice a abstracts of World War I Military Service, 1917-1919 for Michael Casey - not sure if you would also have come across that - it gives us a birth date to work with and an address he was at in New York 1918/1919 - 234 W 30 th Street New York.
Sandra