Fighting Me: Potty Training

I've been trying so hard to be a Proverbs 31 Woman that it's making me crazy.  Being a P31W is not what's driving me crazy, it's what satan has been throwing at me.  His latest is Erin's potty training.  It's been getting to me emotionally really hard.  I know it's not a reflection of how I'm doing as a parent, but there is a little whisper that says differently and compares me to others (or even myself with her earlier accomplishments) whenever I try to reassure myself.  The hardest part for me is that I've blown up at Erin so many times, I know she's lost confidence in me as a safe haven.  I am no longer a safe person for her, she feels.  I don't want her to feel that way, and I certainly don't want her to remember those things.  I'm just so tired of her peeing in her panties.  I don't know why I don't have the strength or willingness to do it, but I don't.  I've prayed about it, too.
But Erin gets sent home every day with a bag full of wet clothes and it really bothers me.  I know they don't want to keep changing her, and they shouldn't have to.  Their rules state that if she can't be dry to send her in a diaper.  So I know they must be getting annoyed. 
The thing is I'm ready to give up and just put her in a diaper for the rest of her days.  But whenever I think about it I know she loves being in big girl panties.  I know she can do this, I just know it.  It just seels like whenever she's out she has a problem.  And she's so strong willed!!!  She won't go when I ask her to even just sit. 
So today, there are two of us home (I was going to send Paul away with Nana and have Erin by myself at home all day, but Chris is home today so that works too).  And I figure we can get this figured.  So far she's been telling us when she needs to go.  I haven't been asking her like a hundred times today, which is nice.  I'm just worried about when we go out.  That seems to be the trouble spots.  I think we're gonna have to go out and get some groceries later today... maybe we will test it then.  If she just went to the bathroom and at least just sat when I asked her to, that would be helpful because then I could just do it whenever we arrive someplace or what not.