I don't believe she dropped it for good, just like that. She just stopped arguing against it during that meeting, after seeing Sylphie accept it and Roxy in tears. For example she really tried to take it out on Rudeus during the sword practice, so she definitely isn't finished with punishing him or complaining, if given a chance. That being said, I have no doubt Roxy will win her over soon enough. She's an experience magic tutor, for example, and Norn could use all help she could get in that. Not to mention Roxy wouldn't try to teach her "genius arts" like the Silent Fitts or Rudeus. The traditional way of doing magic probably suits Norn better.
It was all up to Sylphie to say No or Yes. Having the kids there would have hardly relieved Sylphie from any guilt she might have felt if she had said No. That's what it was all about, ultimately, considering it was Roxy, not just any random woman. She can live with Roxy there to share Rudeus with, but could she have lived with the aftereffects if Roxy had been sent away? It wasn't an emotionally fair decision-making process in that sense. Norn and Aisha didn't really change anything.