M.S.
I would not take her to the Dr. yet. I think I read that most kids do not stay dry at night until the ages of 5-7. Some stay dry earlier, some like me stay wet a lot longer! LOL. I stopped around Highschool along with my brother and sister - it was in our family! My daughter will be 6 in Nov. and I haven't even given it a thought to put her in underwear. She wears pull ups at night and she soaks them everynight. She is a very heavy sleeper. When she gets up in the morning she takes it off, puts it in the garbage and puts on underwear. No wet sheets, no wet clothes. If buying diapers is getting to you, One Step Ahead has resusable night time underwear. We have it and we use them at times, but I noticed they don't work best for soakers, like my daughter.
Hang in there, this is very normal!
M.