Very, very few kids can be "trained" out of peeing in their sleep (enuresis) because it's almost always simply a case of certain body functions not being mature enough to stay dry. This maturation happens at different rates among individual children, most often, somewhere between 1.5 years and 6 years. All but an unfortunate few get there before adolescence.
Here's a list of common causes of bedwetting (from http://kidshealth.org/teen/diseases_conditions/urinary/en...:
Doctors don't always know the exact cause of nocturnal enuresis. They do have some theories, though, on what may contribute to someone developing the condition:
* Hormonal problems. A hormone called antidiuretic hormone, or ADH, causes the body to produce less urine at night. But some people's bodies don't make enough ADH, which means their bodies may produce too much urine while they're sleeping.
* Bladder problems. In some people with enuresis, too many muscle spasms can prevent the bladder from holding a normal amount of urine. Some teens and adults also have relatively small bladders that can't hold a large volume of urine.
* Genetics. Teens with enuresis often have a parent who had the same problem at about the same age. Scientists have identified specific genes that cause enuresis.
* Sleep problems. Some teens may sleep so deeply that they don't wake up when they need to pee
* Medical conditions. Medical conditions that can trigger secondary enuresis include diabetes, constipation, and urinary tract infections. Spinal cord trauma, such as severe stretching of the spinal cord resulting from a fall, sports injury, auto accident, or other event may also play a role in enuresis, although this is rare.
* Psychological problems. Some experts believe that stress can be associated with enuresis. It's not uncommon to feel stressed out during the teenage years, and things such as divorce, the death of a friend or family member, a move to a new town and adapting to a new school and social environment, or family tension can all feel overwhelming.
Doctors don't know exactly why, but more than twice as many guys as girls have enuresis. It is frequently seen in combination with ADHD.
Sounds like your child is still young. Hang in there – she'll probably mature enough to stay dry during sleep sometime in the next couple of years. If kids are still bedwetting by the time they're 5 or 6, it's probably a good thing to have a medical check to make sure there are no underlying problems.
Some kids can be walked to the bathroom during the night, but quality sleep is important to health and development, and not all children will handle this disturbance well. And it's not the same thing as sleeping dry through the night, it's basically one more tradeoff the parents must make in order to cut down on laundry or purchasing overnight diapers.