Can you tell me which companions are fully voice-acted that she will interact with? Also, do you plan on adding interaction with Ruined Tail? Not really a request, I"m just wondering.
Vilja will interact with any npc that have appropriate conversation functions. The majority of companions have what is needed, and in some cases where the conversation files don't work properly in the original mod, I have added in a 'quick-fix' to at least allow Vilja to talk to the companions, even if their replies will be limited.
And you can introduce her to any companion and she will start treating him/her as a part of your household. However, there are some companions that she will treat as unique individuals - if they are in the game and you have introduced Vilja to them, she will call them by name, know some of their stories, and she will talk about them in her dialog with you, the player. These companions are:
Neeshka
Rhianna
Sonia
Arren
Viconia (has not got appropriate conversation functions in the current versions, but I have helped Sulteric to set this up for the next version. Until then, there's a quick-fix in the Vilja mod that will still allow the girls to have some interaction.) *)
Stoker Wolf (has not got appropriate conversation functions, but I have added in a quick-fix in the Vilja mod to allow some interaction)
Saerileth (same as Stoker - quick-fix added to compensate for missing conversation function)
Valeria
Vincente
I haven't added in any unique conversation for Ruined Tails at this point. I feel that this mod is more a quest-mod than a companion mod and it wouldn't be 'fair' to try to add in unique conversation without me getting to 'know' him first. During the summer I will start a new game where I will a) play through the Dark Brotherhood and Thieves questlines in order to write appropriate quest-pvssyr for those and B) play through Ruined Tails and some other companion-oriented questmods. That way, I should be able to add appropriate dialog for interaction.
*) EDIT I just read that Sulteric will release his upgrade of Viconia this weekend - that should mean that she will have a working conversation.