V., I agree with Mindy T. This is not a decision for a para to make, nor was it appropriate for her to have this conversation with you. She should have deferred to her supervising instructor.
As a teacher, we always welcome input from our paras, but a conversation like this would have resulted in a disciplinary action.
Schools cannot retain a child just because a teacher "thinks" she would benefit- there should be solid data available to you that supports retention. Furthermore, just because it worked for another child doesn't mean it will work for YOUR child. Personally, I am against retention except in highly unusual situations.
If your daughter is doing fine academically, move her forward. I think that holding her back to allow her to mature (which is quite subjective anyway) will only frustrate and bore her. She is obviously mature enough to voice an opinion about her education, so I would listen to her! :)
Good luck and keep us posted!