Potty Traing for dummies, Failed

I strive to be a dedicated parent. I try so hard to do what I know I should be doing for my children. Today, I feel like I have failed again as a good parent.I have failed at potty training Savannah again. For the past month I have felt like I have been on the boot camp patrol, making sure that every 20 to 30 minutes Savannah is sitting to the potty, and dreading it every minute in between. Yes, some parts of the day I have gone longer in between bathroom visits for her. Most of the day she has been in panties but, after filling her hamper to the top every other day of damp clothes, at the end of the night she is back in her diaper. When she is in her panties she screams for a diaper. About 5 minutes after she is done sitting on the potty and hasn't gone, she usually has an accident. I am having to drag her to the potty and bribe her to sit on it most every time. She doesn't know when she needs to go and always tells me NO! when I ask her if she needs to go. I don't know why I even ask. When she has an accident she doesn't even realize that her clothes are wet. She wants to keep playing.

I just about had a melt down today after she had wet her fifth pair of bottoms this afternoon. I can't do this anymore. I want to tare my hair out. How do those perfect mothers do it? I feel like I just keep failing her. Savannah is four! In this world, society says that she should be potty trained by now but, I'm just so tired, tired of being frustrated, tired of feeling like a horrible, none consistent mom, tired of fighting with my daughter over something that she just might not be ready for and can't handle yet. I am tired of trying all of the little tricks that other mothers have told me work, and then failing. Why is it that Savnnah can't understand it or want to do it when other kids the little tricks work. I'm embarrassed to say that I've even started bribing her with candy, something I told myself I'd never do. But, I'm just that desperate. I think we'll have her sit on the potty in the mornings and night and then try hard core when school gets out. I just don't know what to do anymore.

Why don't children come with handbooks? Things would definitely be much easier. How do I know when she is ready?