Going through an inlaws library I came across this book. I can't seem to find the name of the signatory anywhere, but the letter suggests that they ran in the same circles as Canadian politicians on the east coast.
It's likely Mrs Hewitt is Elizabeth Borden Hewitt, daughter of Sir Frederick Borden. She married Charles Gordon Hewitt in October of 1911, right after the September 1911 election.
/u/canadianhistorian is completely correct!!
Elizabeth Borden was born in Canning Nova Scotia, Daughter of Sir Frederick Borden, a very wealthy businessman, he made a significant amount of his money on ships (particularly ships that carried Bird Guano form the south to the north to be used as fertilizer on farms). He later became one of the best know Ministers of Militia in Canada prior to WW1.
Elizabeth Borden Married Charles Gordon Hewitt right after her Father's party lost the election in 1911. They lived in Ottawa, however from the records I can find she returned to Nova Scotia after her's husband's untimely death in 1920. If you want more information about her I can call a friend who works in the Kings County archive. Her will is on file with the probate office.
Here is her portrait done in 1910 http://www.artnet.com/artists/frank-hector-tompkins/the-pink-shawl-portrait-of-elizabeth-borden-AmAKiGZCUzATvHBKnZQhDA2
Also her last name was spelt differently on different records either HEWETT(sic) or HEWITT!