Night-time "dryness" is biological based, and can take until even 7 years old. This is normal. This is per Pediatricians.
Night time dryness is not the same as day time toileting.
It is good you are understanding that she still is fine to wear diapers at night. Even at 5 years old, my daughter was wearing night diapers.
And I have like 4 waterproof bedpads, that I put under her, in case of accidents. Not all 4, but of course just one. Easier clean up that way.
The waterproof bed-pads I got from Amazon. They have all kinds.
My daughter, when she was already 5 years old... just one day said she was "ready" to just wear panties at night. And indeed she was. By then, she was developed enough mentally and biologically... to wake herself and go to the bathroom by herself. To know... she had to pee. Even if sleeping.
Your daughter is still wet at night... which is normal. She is only 3. My son is 3.5 years old and he is wet too, at night and for naps. He wears diapers for sleep.
Maybe... put on her underwear... and then she will see, that she still wets. or, put on her underwear over her diaper. Or put her underwear on under her diaper. I have heard of some that do that.
all the best,
Susan