K. J,
I know several moms have already said this, but I want to reiterate that it could be constipation causing this, in which case, she really isn't aware of it. Even if she is having bowel movements, she could have a build-up of poop in her system that is causing leakage, or her poop could be so dry and hard that it starts to come out before she gets to the potty. It's not a choice, if that's the case! So I hope you will really give this serious consideration and maybe take her to the pediatrician to be checked. If it doesn't seem to be constipation, perhaps hearing about cleanliness from the doctor will make a bigger impact on her and gave more validity to what you've been saying! And the wipes idea is a great one, too.
The other thing I would say is, it is not unusual for kids her age to be "lazy" about homework, etc. Sometimes, regardless of how it looks to our frustrated selves, they are truly overwhelmed with all of our expectations! They just don't always know how to get started or stay on track. I'm learning with my seven year old that I have to really model it and walk through it with her, over and over - "it" being, cleaning/straightening her room, organizing toys and books, getting through all her homework, and putting her clothes and shoes where they belong. Some children just need more hands-on time with this. My girl is very smart, but what that does sometimes is make me expect too much of her. When we finally calm down and talk, I will often realize she truly didn't understand what I was saying, or how to do it. So - saying this as one who needs it, too! - I would just encourage more patience and calmness, less judgmental feelings towards them, and then check into the likelihood of constipation. Also, sometimes we think they are lying when they are just telling us their understanding of reality. I'm not trying to make excuses; this is another thing I've learned the hard way. And I had to learn it, even having studied early childhood in school! Now, she may really be lying, but it's very, very possible that she is telling the truth, in which case, we wind up creating emotional problems for our child if we think of them as lazy and lying. So what was just a physical problem (body isn't working right because of a build-up of poop) becomes a true, psychological issue because of how the parents respond. I say this only because I have been through this, and am still going through it, with my seven year old, who has serious constipation problems. I have often found myself making harsh judgments about her (who sounds a lot like your 3rd grader!) before realizing she needs more time from me, more support and encouragement, and really, more help. Good luck! Meanwhile, Oxy Clean works good on stains. ;)
Peace to you,
S.
(also, a fiber chew or Miralax might be worth using for awhile, to see if it helps)