Some people believed that if they woke up in the morning in a bad mood, they would be in a bad mood the whole day. Maybe it was just a suggestion made by the brain, but some people did experience it.
Princess Ievna didn't even sleep last night. She indeed turned into a red rose at night, but that didn't mean she would sleep in her red rose form. Instead, she would stay up all night in her red rose form.
That was the strange effect brought by the witch's curse, but Princess Ievna indeed did not need to sleep at night when she was in her red rose form.
When she was just cursed by Sharass fourteen years ago, she was very anxious because she couldn't sleep at night when she was in the form of a red rose. But then Sharass told her that she was no longer a human who needed a good night's sleep, and that was why she had to stay awake in her red rose form.