"How do we know she is still alive? Because Locke hadn't sene her for years. Then he hires a private eye to find out if this woman who comes to him is his real mother. He tells him yes, and a DNA match is positive, and then CONVENIENTLY slides a dossier of his real father to him. (This was episode 1.19, http://abc.go.com/primetime/lost/index?pn=recap#t=38115&d=40651). Remember his dad was a rich CONMAN, and could have hired someone to pretend she was his mother, then paid off the private eye after he found out which one Locke went to. All a big con to get Locke to give up his kidney.
We do his Locke's mother in the hospital after he was born, so we know she survived his childbirth. However, Locke is obviously older than Ben, and thus the mother still could have died giving birth to Ben at a later date."

"Right, we know that someone came to Locke that he believed was his mother. I think BigRollTide's point was that the person we see Locke with as an adult may possibly have been pretending to be his mother."