I never really found her to have much personality beyond sweet, wide eyed and super intelligent. Now maybe that's enough for some people but it didn't grab me.
I do think there could have been a huge amount of work done with only living for 9 years if they had her on a 7 year show. She could have been quite aged in seasons 6 and 7, if she was in a relationship there would have been those issues etc.. many things could have been done with this. I do not think she would have stayed with Tom if she had paired with him as she would have outgrown him intellectuality and emotionally in a month at her rate of development.
Really it's like the Maquis storyline, would have taken long term planning and infused the show and for whatever reason they just didn't want that.