Buy some waterproof bed pads to put directly under her when she sleeps.
It makes clean up WAY easy.
I have about 4 of them that I got from Amazon.
My kids' sheets are never soiled because I use the bed pads.
My kids are 5 and 9.
My daughter was having night accidents even at 7 years old. Even if she was potty trained from 2 years old.
My son still wears nighttime diapers.
NORMAL.
Childhood, is never, finite.
AND childhood also means, they have pee accidents.
ALL of my Daughter's Teachers... from Preschool to Kindergarten to 1st Grade, ALSO said that kids at these ages have accidents- at night or at school too. It is childhood. They have accidents. It is normal.
Accidents happens even until 7 years old and per Pediatrician's this is normal as well.
Again, nothing is finite in a child. It is not a one-way developmental direction. Mistakes happens. Physiological development is still happening as well. And fear of "back sliding" is only going to make it worse. For her. And you all.
Because, this is not "back sliding." This is, NORMAL, pee accidents.
Or she is a very deep sleeper.
And personally, I do not believe in waking a child all night just to go pee. They get lack of sleep.
Just get waterproof bed pads, and use a night time diaper for now.
What you are experiencing is common.
It is childhood.
I know of no child.... that has never had a pee accident.
Then before you know it, it is a thing of the past.
Again, night time dryness is something that is not attained until even 7 years old.
Your child is only 3.5 years old.