My eldest had this problem, the advice we got from the enurisis clinic was this:
Drink as much fluid as she can during the day, (sometimes its also to do with bladder capacity so drinking lots during the day will help her hold more if that makes sense) if you let school know discreetly they may let her have more access to her water bottle.
Sips of water after tea time (don't drink milk -can't remember why but just told not milk)
Go to the toilet before bed, relax on the toilet and count to 20 ie pass urine slowly rather than rushing as my DD used to do, then get her to clean her teeth and then go back again to the toilet (sounds like a bit of a nuisance but this will ensure the bladder is empty).
If she does wet the bed clothes, ask her to help you strip the bed (I was horrified when they first said this but apparently it is supposed to help train the brain, it's not meant as a punishment).
Most importantly don't make a huge fuss over it, she will get there eventually
Doctors won't usually do anything till about 7 or 8 years old, health visitors or school nurse may also be able to offer advice, ours ran an enurisis clinic.
Hope this helps, good luck xx