I've been where you are, and it sucks.
There's a hormone called ADH that you produce while you're sleeping that stops you from producing as much urine while you're asleep. Some kids don't start producing this hormone until later in childhood, some not even until puberty.
For most bedwetters, this is whats happening, and all the alarms, lifting in the night, no drinks after 6pm will make no difference whatsoever, as their bodies don't have the ability to regulate this.
My daughter didn't stop bed wetting until she was about 10 and a half, but when she stopped she just stopped. She had about 5 accidents in the 2 years after, and nothing in nearly 2 more years since then.
Keep trying the GP every year or so, I seem to remember they start looking into it a bit more seriously when they turn 9 or 10, just in case it's a bladder issue.
The most important thing is not to make her ashamed of it. Just get up, change the sheets, and back to bed.
It sucks, and at times you will feel like tearing your hair out at all the washing that needs doing but it's not her fault and it will pass at some point