My son did the same thing. I have heard it is pretty common for kids to do this. We told our son that it was better for him if he wears the pull-ups just a little longer. Try to make your daughter see it, not as punishment that she has to start wearing them again, but b/c you love her and you want to help her have a good-night sleep and not wake up with tee-tee all over her. We let our son pick out the design of his pull-ups and even had a little sticker calendar where he put stickers on the days he didn't have an accident. Once he reached a certain goal, we let him pick out some new underwear. Before we knew it, he stopped wetting the bed and for good this time.
Also, something to try when you are at home with your daughter during the day....I love the sing and read series from Frog Street Press. They do colors, numbers, alphabet, nursery rhymes, etc... They even have reproducible activities and ideas to do that go along with each lesson. I bet your 4 month old would like the music too :) I got my sets off of E-Bay, but they also sell them at www.frogstreet.com