May be you have to check why. She did well before you change maid. Will this the cause? If so, don't only frighten her. It may even worse because this is 心理問題.
Check out why before you take action.
Agreed with Barbara. Some children will exhibit regressive behaviors (倒退行為) when they are distressed or feel threatened, such as become clingy, or even wet their beds. Your child might be upset by the departure of the maid. If so, alleviating her distress or fear will reduce her wetting behavior.
So, first of all, you have to check out the underlying reason(s) for the child's wetting behavior.
Sometimes it may not be the child do not want to. Personnal feel this may physically ready or not.
Take my two sons as an example.
The eldest one stop wetting the diaper since he was 3years old. He is a size XL kid. We took away the diaper and he never wet his bed since then.
The small one is now 4.25, a M size boy! We tried to train him as his bother at 3 but failed. Earlier this year, we found he didn't wet the diaper and ask him not to use the diaper. He said yes but he still sometimes wet the bed. He want to use the diaper again. By summer, he himself said he does not want to use diaper. I ask him not to wet the bed. He has to go to toilet himself. He did wet the bed for few times. However, I find he is going well. His bed keep dry for two months.