She's still little enough that her peeing at night isn't a big deal. I have a 4 year old that is day trained, but not night trained. It takes some kids longer for that "wake up" part of their brain to mature enough to wake them up instead of peeing in their sleep. If you're really concerned, call your doctor, but like one of the other comments said- they probably won't do anything to intervene until your child is 10 or older. (I was one of those really late ones, and have memories of that 'wet sensor alarm' going off in the night. Yikes, that thing was scary! I wouldn't do that to a little kid, ever. It was bad enough for me, and I was around age 10. Basically it's a device that helps train the brain to wake up before you pee.)
To minimize laundry, get one of those waterproof flannel pad things that they have for cribs, and put it on top of her sheet. Limit fluids at bedtime, and try a nighttime pullup - I found that pullups for nighttime seem to prevent leaks better than diapers do with the older toddlers.