I hope the other ladies who posted read my response. Pull-ups do not cause children to wet the bed longer, they just keep you from getting upset over having to change the bed every morning. Decide what you want, a soaked bed every morning for several months or a wet pull-up. Which is easier for you and your daughter? Don't make life any harder than it is.
Bedwetting can be inherited, so check your family and your daughter's father's family to see if there were any bedwetters.
Doctor's aren't concerned about kids not staying dry all night long until they are 6 years old. The average age for girls to achieve nighttime dryness is four; boys achieve it about five. Or, if your mother keeps you dehydrated like mine did, earlier.
My daughter was a bit older than four when she achieved nighttime dryness. I used the pull-ups a couple of months after that because she is a very sound sleeper and hadn't learned to get up at night if she needed to. Also, she had a bed rail, and it would take her a little longer to get out of bed (though wetting the bed once convinced her she didn't need the bed rail anymore). At the end of October 2007 she asked to wear her big girl panties to bed, and she has had only two accidents since (including the bed rail incident).
What actually has to happen is that your daughter needs to start producing a hormone called anti-diuretic hormone in order to stay dry all night. In some kids it happens right around achieving daytime control. But in a lot of kids it takes longer to develop, sometimes a lot longer. My daughter has it in spades now, because she can stay dry all night long, then go another 45 minutes after she wakes up before she has to urinate. She has also learned to get up and use the little potty in her room if she needs to urinate at night (something I reccommend, so your daughter doesn't have to rush to the bathroom in the middle of the night; very handy having a potty right there).
I also would take my daughter to the potty before I went to bed (she never really woke up) then her dad would take her again when he got up in the morning (around 5:00 am). When I notice her urine production was diminishing at 11:00pm, I set my alarm and got her up at 2:00am (yeah, it was tough staying up late or getting up at 2:00, but it was better than having her hysterical in the morning because she wet the bed). When her 2:00am production was getting less, I decided to let her go all night without waking her up and she has been perfect. I think getting her up at night helped her learn how to get herself up. I restrict her liquids after dinner (unless she has been very active and obviously thirsty, but I stll restrict it to a couple of ounces) and she goes potty right before she goes to bed.
Scientific studies have been conducted that prove some kids are very sound sleepers and don't register when they need to relieve themselves at night. If the child has been dry then starts wetting again, it is a symptom of sleep apnea because when they do sleep, they sleep so deeply that they don't realize they've wet themselves.
You can get a very nice, not hot, waterproof mattress cover at Linens 'n Things. It's a bit expensive, but it saves a lot of worry about ruining the mattress. My daughter is a hot sleeper so I wanted a mattress cover that wasn't to plasticy to make her hotter. Your daughter may be too young for an alarm pad. It might scare her. But if she is delayed in achieving dryness, it might be something to consider.
I am not an expert, I just know what worked for my daughter. I got most of my information from wwww.childdevelopmentinfo.com/disorders/bedwetting.shtml This website has a very good explanation of how anit-diuretic hormone works.
It may just take you daughter awhile to achieve nighttime dryness. Please be patient.