Don't be too hard on yourself. I broke down several times in front of my son. Every mom has been where you are. Just keep trying.
Here are some things to try:
1. When you take her to the bathroom, have her sit on the training potty for 5m. Set the kitchen timer if you have to. Leave her sitting there if you have to. Tell her that you will be right back.
2. Keep spare clothes in the bathroom.
3. When she messes, only change her IN the bathroom. Give her a wipe down with a washcloth or a quick shower rinse if you need to.
4. Put a pull up on her OVER her panties. This way when she does wet, she will feel it, be uncomfortable, but not get pee everywhere.
5. Buy the flushable wipes. They are a life saver!
When she does have an accident, don't hurry to clean it up or her. Don't leave her sitting in wet clothes, but don't 'rush right to it'. Make her walk to her room to get fresh panties and clothes - keep them where she can reach them. Don't carry her and don't rush. Let her feel the cold and be uncomfortable.
Hugs
M.