My two big kids learned on little training potties. My second one would hold it and then it would become this big issue, much like yours (but she was 4). So, things I tried: potty training books of all sorts, in a basket next to her potty to read while trying to go. Or, these days we have tablets, she can watch a show and just kinda relax or zone out a bit. If these little tricks aren’t helping - let her go in the pull up - then progress to pull up, but in the bathroom, then try on the potty with a pull up , then try the hole in the pull up trick. I still would use the little potty, it just seems less daunting. Good luck