Not sure if there's a connection, but I'm searching for a Walter Horwood (b. 1901, parents Fred and Florence Horwood) who left Liverpool and arrived in Quebec on the Vancouver in 1907.
They would have been traveling the same route as the Empress, and they were also a Salvation Army family. I'm trying to figure out where Walter's family was from in England. I just found out about the SA connection a few days ago using the Ancestry.com at the library (I only have the USA version).
Walter ended up out in Calgary with his parents marrying Hazel Smith, and they moved to Vancouver, British Columbia. Unfortunately, I have not been able to order a death cert for Walter since they are $40 for those of us south of the border, and I just lost my job.
I'll keep digging. Walter and Mabel were born within years of each other. Perhaps, if not brother and sister, they might have been related some other fashion.