LOL I just saw the date I bet you solved the problem now!!!
Diapers at 8 years old is Punishment.
The more you punish the longer the wetting will last, find out why she is doing it, there will be a reason, she is possibly feeling upset about something, has a new Baby come along ,new school, new house, area, something that could have had an emotional effect, this calls for the opposite of punishment , and how about you let it go and dont make an issue about it.ask Dad to play games and sports and get some Physical activities going.
After researching bedwetting and daytime wetting on the internet, I learned that there are some different reasons why toliet trained kids soil their pants. I read that this is something they cannot control and should not be punished for it. Some kids have small bladders, so when they are full they explode. They lack the hormone that tells the brain that the bladder is full and needs to emptyed.
If your child is not going through something emotional that is causing this, I would take a different approach, maybe some councelling, the reward system.
You should ask your doctor about DDAVP...read more at this link to see what is it. http://en.wikipedia.org/wiki/Desmopressin
I too am dealing with the same problem with my 4 1/2 year old. My doctor put her on DDAVP. She has only been on it for a month now, and it is not working yet, but it takes time. My son was a bedwetter, we put him on the same medication...3 months later he stopped and never has accidents anymore.
Good luck!
Try a praise and reward system. Go through a toy store, and find that special toy that she really wants (set a price limit though) and tell her if she can go x days in a row with out wetting herself then she can earn a sticker or something towards the prize.
Personally it sounds to me like if it is not medically related she is seeking attention. If there is a change in the house (a split up between parents) no matter how long it had happened, or perhaps she saw something on tv that really disturbed her and she doesnt know how to communicate. And/or a possible younger sibling in diapers and jealousy.. There are numerous things that can change a childs behaviour such as this.
For my sister when we were younger and she did this, it was because we moved a lot and she did not cope well with forming/losing relationships with peers.