I am dying to know who Luffy's mom was. So, here is my thoery. Luffy's mom died when Luffy was around 3 or 4 and therefore does not remember her. She was most likely a regular person but, here comes Dragon, Dragon left to go start and/or contine the revolutionaries and his wife - Luffy's mom - understood that. (She obviously agreed with him on the World Goverment otherwise they would have never stayed in the same room let alone gotten married. So she is NOT a marine.)
X - A marine (As I said before she would have to agree on the World Goverment with Dragon otherwise they would have never stayed in the same room let alone gotten married.)
X - A revolutionary (I doubt she would be pregnet and then lug aronud a baby while fighting the World Goverment. And even if she was a desk jockie marines could barg in guns blazing at any moment.)
X - Alive (Would any mother let their child be raised by Garp while they're still alive?)
/ <-- (That means maybe.) - A normal person (Honestly I think she is just some normal person who shared the same views as Dragon and when she met him...You can probably guess the rest.)
So on what she was/is (not complely repealing the idea that she is indeed alive but just saying it's highly unlikely) I think she was a regular person who is now dead.