"I am only in first class because this little one is too small for me to be elsewhere in the middle of the night."

Which is true. Edith also needs Jyn's help oftentimes but Jyn is very loyal to Edith and knows better than to mention that in what is technically a public place. Edith comes from old money, but she is young, and Martin simply doesn't care about rich people. He is a builder at heart, an architect by trade, and Jyn knows he would rather spend his time speaking to the Irish shipbuilders than his and Edith's first class dinner companions. They all eat breakfast together, Jyn included, but not on the ship.

"You won't see me in the first class dining room or the church services." First class in name only because of all the other rich society people on board.