Re: 4 year old suddenly wet every night?
Often, it's brought on by stress. You usually notice this more in school age kids who are feeling stressed about work at school, or something coming up that they need to improve on. But perhaps she's overthinking something?
Also, when it's cold, we tend to sleep harder, and kids will dream they are on the toilet and then wet the bed.
Possibly, she's just getting lazy, because she has the pullup on. Why get out of a warm bed if you have that backup?