User blog comment:Steven+Amethyst=SmokyQuartz/Down with the World Nobles/@comment-25400375-20170218034229/@comment-24850639-20170220214816

Here's something we definitely don't know for sure, but I feel 100% comfortable with assuming:

If Luffy's mother was someone who was truly of no consequence to the actual story, or to Luffy's growth as a character, Oda would have definitely had no qualms introducing us to her very early on in the story. Same goes for Dragon, same goes for Garp. Instead we get Makino as a mother figure, Shanks as somewhat of a father figure. We don't learn Luffy even has a dad until we learn that he has a Grandpa! 300 something chapters into the story. We saw Garp first in Chapter 92, Dragon first in Chapter 100. Not simply just to play with us, but to show us more about the world in general so that we had an actual idea of how important these people actually were when we met them. By ch. 92 there was no reason to believe that the crew was ready to tangle with Vice Admirals, and by ch. 100 we didn't understand enough about the history of the WG to realize the importance of the existance of a group like the Revolutionaries. Whatever Luffy's mom is, I don't think Oda would have waited this long just to show us that she's some kind of widow of no importance, or that she's just another revolutionary. So with that said, I do feel comfortable assuming that she identifies with a group that Oda has not shown us much of yet, but is important enough to the world in general that Dragon and Luffy's connections with her are on the hush. My 2 biggest guesses, are either the Celestial Dragons, or the D. Clan. I could see both backgrounds being stooped in enough tragedy that Dragon and Luffy's mother would take steps to protect their offspring.