GuillotineCalamity seems to be connected to Tachyon and has posted several videos in response to the OpAphid Alternate Reality Game. Guillotine Calamity says her name is Sister, but her first initial is "L." Despite her numerous responses to OpAphid and Tachyon videos, GuillotineCalamity is fan fiction and not an official part of the OpAphid ARG (per her own admission).
The GuillotineCalamity Arc
The GC Arc revolves around a community run by "W," otherwise known as Wolffe Walker. W is the grandfather of Sister, or L, as well as Caroline Walker. It is not yet known how this community relates to Bree's or even OpAphid's. In the video Bedtime Story, Sister discloses that Caroline came across or was involved in some sort of ritual in the woods bordering Grandfather's (W's) land. She returned battered and bruised, and heard the voices of a "Cassandra" and a "Helena" in her head. The speculation is that they belonged to Cassie and Helena Petrovna Blatavsky, whose works influenced Aleister Crowley. She later committed suicide.
According to her videos, Sister is out for revenge. It is unknown at this time exactly who she is working for.
GC Canon Characters
GuillotineCalamity - Sister herself Itrog - Antoinette or Marie, an old friend serveshallslaves - Simon, an old friend who deserted the community autumnriley - Riley, always loyal to the community CredoWw - Wolffe (W), Sister's grandfather and the head of the community TheLadyLazarus - Lady Lazarus, connection still under speculation
OpGrey - An unknown operation. Sister denies contact, but the anagram was in her She's Got Nothing On Me video. OpGrey anagrams to "Go Prey," which is in a couple of Sister's videos as well. codesintoveritas - Eli, who seems to know Riley. Riley's video, The Search for Veritas, seems to indicate that there is a connection.
Codename Triple Knot - an ARG support forum which focuses heavily on GuillotineCalamity as well as OpAphid, Tachyon, and the rest of the Breeniverse. xposingcalamity - Kevin, a fan who watches Sister and shares what he's decoded.  - Sister's blogger, which has information about Helena.