I looked up a the Sharon Cassidy follower in the wiki and noticed there are supposed to be Voice over narrations and cut scenes. For example, when you complete "HeartAche by the Number" peacefully by exposing the Van Graffs and Alice McLafferty to the NCR authorities, there's supposed to be a cutscene with Cass standing with rolling hills in the background. Then you're supposed to hear a voiceover narration that goes:
"In the years following the destruction of Cassidy Caravans, NCR used evidence of the plot to blackmail the Crimson Caravan and the Van Graffs. NCR enacted strict trade laws with little resistance, strengthening their supply lines and their position in the Mojave."

However, this didn't happen when I completed the quest. Has anyone else had this issue, or some could it be a mod problem?

Mods I use are:-

• Beware of Girl Type 3
  
• sixy Lingerie for type 3 (Lingerie - 2.0.esp). - I noticed this one, by Guinness, is not on Nexus anymore, unless there has been a database glitch.
  
• NV Type 3 Armors only
  
• Conelrad Civil Defence Radio
  
• Bugfix - community Patch DE (not the one from Nexus, as a comment says that one is out of date since official updates). Compiled Patch.esp (marked as a master)
  
• Navada Skies (NSkies - Vanilla Edition.esp)
  
• Ling's Coiffure (Lings.esm)
  
• New Vegas Error Corrections - Reduce CDT (No DLC.esp version). With fix for Lings.
  
• Jewelery for type 3 (Jewelery.esp)
  
• Pin Up Girls Deck V2
  
• Real Life Pinup playing Cards - Gormorrah
  
• And my own which doesn't change anything like this. It just adds hair from Lings, and gives followers a relax mode.

It happens in the end game during the end game cutscenes. However, if you kill the Van Graffs at any point after that quest, you cannot get this scene.