6 year old wetting bed and self.

My step-daughter is 6 years old and still wears a pull-up to bed and have frequent accidents during the day.  She is only with us every other week. She lives mostly with her mother, grandmother, and sister.  I thought it was odd when I met them that she was still having these accidents.  My husband said she was potty trained, but still had accidents when she was little.  They brought her to the doctors and he said she would grow out of it and that there was nothing wrong physically with her. I have tried waking her up at night to get her to go, but then she's already gone before I get her up.  I remind her hourly to go potty, I don't let her have water after 8:00p.m., and I don't over react when she does potty on herself.  Yet she still have frequent accidents.  This week she has gone at least four times on herself during the day.  She also cannot sleep without a pull-up on. She told me the other day that she waited last minute and then sometimes she says she doesn't feel it.  I am torn because I do not know whether she is being lazy and waits last minute or if she honestly cannot feel it.  I don't know what else to do.  I am new at this whole mom thing, marrying a man with two daughters so I am looking for advice everywhere on this subject.  I talked with her mom, but I just feel there's something more I can be doing I just don't know what it is.  I also know that there has to be something done at her moms though.  Can anyone lend any advice? Medical and Motherly?