Izzie sounds a lot like my DD1. She had no trouble getting the wee down and only had minimal accidents once she got the hang of it--it helped that DH and I were on the same page, so she got consistency from everyone. The poo, however, took longer. She just seemed to either not get her head around it or sometimes freaked out trying to do it on the toilet. I had several months of messy pants and accidents and just wanted to pull my hair out sometimes. She was potty trained and doing well, but just couldn't seem to get this one thing, and it brought me to despair at times--especially when she had accidents in nursery.
I finally just kind of sucked it up and let the accidents happen. I would clean her up and try so hard not to be all negative if she had an accident as I knew this would make it worse, and it's better she has an accident than she learns to hold it and not go at all--causing bowel troubles. We also adapted the reward charts to find things that were meaningful to her to reward her if she went on the toilet. We had done that during her initial week or two with the wee, but we changed it to be just rewards for the poop. For DD, sweeties didn't seem to make a huge difference, although she loved getting a Peppa Pig sticker to put on her chart. At first some of the rewards came for when she had a bit of an accident, but she still managed to get some poop in the toilet, then it finally shifted and she got the hang of it.
Those months weren't fun, that's for certain, but you will get through them, and she will learn eventually, I promise! It will help tonnes if you and DH can get on the same page--sounds like you are making some strides there.