I have boy/girl twins.
Both potty trained in the day at just over 3 years, but continued to soak pull ups at night. Some nights they'd fill the pull ups so much they'd leak.
We had a dry spell at 4 years old with DD, but DS was struggling with various things and I decided to keep them both in pull ups at night because I didn't want to add another thing he couldn't do to his list. I sort of regret that now.
We (the children and I) always had a plan that we'd try with no pull ups after three dry pull ups on waking. This was partly to stop them wanting to try after a single dry morning (it just meant wet beds the next night every time) and partly to give them an incentive to get up on waking and use the loo rather than be lazy and use the pull up, which I think was happening. We had a few three-day dry spells with each of them and tried for a week after each, but always ended up back in pull ups.
At 6.5 years DS had three dry pull ups and tried without. We have had less than 10 accidents in the night since then (nearly 8 now).
DD is still in pull ups and still fills them every night. I am hopeful it will just happen like it did for DS, but it is starting to get her down now that things like Beaver Camp are on offer and she's reluctant to go partly because of the pull ups. She's terrified her twin brother will tell someone at school 
I am reluctant to try the alarm as I don't think it will work for DD. Like someone else said, she sleeps so deeply I think it'll wake me not her! I would like to try the desmopressin route, but am wary of making it a bigger thing for DD by taking her to the GP if they're not going to help.
For what it's worth, I was a bed wetter until at least 9/10 years. I remember taking a plastic sheet to sleepovers (long before the days of pull ups for primary school kids). So maybe it's hereditary, which could fit with the hormone development reasons for wetting.