She is 4.
Even if potty trained when younger, she is only 4.
When they are young like this....they don't have full impulse control yet. Nor can they... "estimate" how long... they can hold it. Nor how long they can wait or not, until they really have to go versus when it is too late. They can't estimate that, like an adult can.
Accidents happen.
It is childhood.
At this age, this commonly happens.
Even in Kindergarten.
I work at a school.
I know.
ALL of my daughter's teachers, from Preschool to Kindergarten to 1st grade, said that kids these ages, have accidents. And if/when a child has an accident in school, the teachers make no fuss about it. Kids bring extra clothing to school, for this reason. They have accidents.
Even at night, they are still in night-time diapers too. Night time bladder/hormone/myelin sheath development, is different. It is physiological based, not age based.
Both my kids had accidents too. In Preschool and at school.
And, "stress" CAN MAKE the child, have more accidents.
ie: like when I had my 2nd child. My daughter, had more accidents. Their emotions are not even, fully developed, yet, at this age. Either.
Just let it be.
As I said, ALL of my kids' teachers, said that, kids these ages have accidents. It is childhood.
It does not matter, how long a child was potty trained before.
Each age stage, differs and cognitively too.
Is your child in Preschool?
At my son's Preschool, even at this age and older, they helped the kids with pottying. And it was no big deal. My son was 3'ish when he even began, to potty train. We went by his, cues. And his body.
And his Preschool did too, and they were very nurturing about it.
Or try leaving her naked, on the bottom when at home.
We did that with my kids.
And then kept the potty chair near them, in whatever room they were in.
And we did not nag about it.
And they began to use it on their own and then increased in frequency and skill, in using it.