Once you finish her main collar search quests. Depending if you reached Lover or Soulmate level with her you may have unlocked her Intimate or Undressing actions.
Additionally, she will tell you you can bring her any extra collars (there's like 3 additional common collars) you can find and that will unlock an extra sex scene. This is also a second chance to raise her friendship level further in case you didn't reach Soulmate with her the first time.