M.B.
You are absolutely right that spanking is way too harsh. It sounds to me like your daughter wasn't ready and she's rebelling because you controlled the process and not her. I would put her back in pullups and let her know that when she's ready to use the potty, then she can wear panties again. But, let her know it's not okay to pee all over the house. If she doesn't want to pee on the potty, she must pullups or a diaper. It's clearly a control issue. Set the rules, but let her control going to the potty. It's okay to ask her if she needs to potty, but taking her to the potty ever 30 minutes isn't going to teach her to tune into her body's signals. I kept my boys in the thick training underpants while they were starting to use the potty and when they're really ready, accidents are rare (and usually not at home, but when you're out somewhere and can't get to a potty quick enough).