Two is pretty young to be 100% potty trained, so first of all, I wouldn't worry too much. I know it's a hassle to keep cleaning up messes, but it will just take time. Secondly, going #2 in the toilet is a BIG deal for kids. All 4 of my girls were scared by it at first. I don't know if they feel like their body's falling apart or what!
I would just make sure to have her "help" with the clean up. Take th panties into the bathroom and dump out the mess into the toilet and say stuff like, "THAT is where that belongs!" or "yay! It get's to go in the potty now!"
I wouldn't try to make her feel too bad or "naughty" about going in her pants. She may not have the muscle control or be brave enough to do it in the potty just yet. When and if she does go in the potty, you're going to have to make a REALLY big deal about it! (Jump up and down clapping and singing, tell Daddy or Grandma "guess what she did today?", big hugs, etc.)
My oldest used to LOVE stickers. I had a big sheet of paper on the wall in the bathroom by her potty, and whenever she went, she got to put a sticker on her "potty chart" (not really a chart, but she didn't know the difference!) Maybe you could do something like that and give her 2 stickers for going poo-poo.