Should I try harder?

My 3 1/2 daughter has mild SPD (mostly under responsive) and no interest in using the potty, although I don't think that she is afraid of it.

For the last four months, I've noticed that she holds her urine while at preschool or whenever she is outside of her home or away from me. On a recent vacation, she held it for about 20 hours. (She might have been a bit low on fluids, but not to that extent.)

I haven't pushed the issue much because if she can hold her urine for hours, there is no way that she is just going to go if I put her on the toilet every so often. She knows when she is wet and seems to understands the process. She rarely indicates that she is wet or soiled though. She clearly does not want to go while on the pot. I have dangled some very enticing carrots and yet she still does not see using the potty as an option.

She does not like getting her feet wet when wearing underpants and knowing that, I think that she holds it while wearing them. Should I just try the underwear again and see what happens?