Hav eyou properly cleaned the area thoroughly? Do you give her ANY attention for peeing on the bed? Even if it is "NO! BAD DOG!" that is still giving her attention.

Gate the room, or keep the door closed. This is the same concept as potty training a toddler and they wet the bed. They don't realize it and can't help it sometimes.

Just go back to basics! Clean the bed, covers, and mattress THOROUGHLY with a cleanser for pet urine that contains stuff to get rid of enzymes and that area will no longer be favorable for her to pee. Regular soap and water gets rid of the smell, but not enzymes that dogs can smell and those indicate "hey, pee here" so they will continue peeing in the same spot.

EDIT: Also, this will only be a lifelong "problem" if you are not consistant in training her entire life. You need to be consistant and get her on a schedule, that will REALLY help