Regardless if you like the character or not, she did bring a very interesting bit of drama that TNG lacked. The TNG command clique through all seven seasons for the most part lived in a bubble, where they're all happy go lucky and are fairly harsh towards all outsiders.
Shelby did penetrate the bubble and did shake things up. She brought a sense of conflict and drama to the command crew that was entertaining and refreshing for TNG. The only person that did this better was really Jellico.