I think for a bit after the split it was possible to believe that they had one consciousness that hopped bodies – Sue was marveling at her new body, she knew exactly what she had to do when she woke up and knew why she was there, and on the first switch it was kept ambiguous what Elizabeth knew or didn't know – but after they had switched back and forth for the second time it was clear, as you noted, that starting from the split, they had separate experiences and consciousnesses and could only speculate from the traces of the other's actions.
Sue hated Harvey, but all she wanted was to get back to being famous and adored, the only thing that had ever brought her joy and meaning. I'm sure it's not the first time she had to work with and be at the whim of someone she hated.
Getting the job back herself, without him even knowing it, was the only form of revenge that was available to her.
Neither Sue nor Elizabeth even had the decency to dress the other and make her comfortable, she was so self-obsessed that she didn't have any consideration even for herself.
She hated not only Harvey, but also herself and her aging, and that's why she could never be One, and why the Balance never had the slightest chance of working out.