I always thought of it as Warakia Arcueid since she does share some similarities (personality-wise with Wara).
Now, this next part is based SOLELY on the text and info from the Melty Blood fighting games. I've only played Tsukihime for about 10 minutes and I have no read the manga or watched the anime, so bare with me if I'm wrong (there are probably more correct answers than this one), but this is what I have observed concerning the games and the names... Come to think of it, way back in Melty Blood ReACT she never had an official name. She was just another form of Arc and was called Arcueid Brunestud along with the original Arc in the Chara Select screen (and on the VS screen too). When the English patch came out her replay data abbreviated her as simply Warc in MBR (maybe because of something said in the game of Tsukihime and/or the manga of Tsukihime). When Act Cadenza came out Type-Moon officially differentiated her as Red Arcueid. So if you ask me, it goes way back to the original Melty Blood, Melty Blood ReACT, and most likely something in the depths of Tsukihime, and also the fact that these three games have been translated and played by many WAAAAAY before MBAC officially gave these characters some individuality (name-wise). So, I think Warc just caught on and became more popular than Red Arcueid because of that previous fact. I mean, Warcueid sounds badass right?
Same with V.Sion, and the fact that MBAC PS2 was released well before MBR was translated. In MBR she was just called Sion Eltnam Atlasia in a vampire form before the patch. In the English translation she was called V.Sion in the replay data (because of the reference from MBAC PS2 calling her V.Sion in the options menu I suppose). The name thing is the same with Akiha Tohno and Akiha Vermilion too if I'm not mistaken. Sion TATARI was V.Sion's official name in MBAC PS2 on the character select screen, and in the VS screen, but in the options menu she was called V.Sion. I guess V.Sion sounded cooler amongst fans and the fact that it could have been referenced in Tsukihime too (it most likely did). Warc was called Red Arcueid throughout the game (MBAC PS2) and in MBAC PC, but many just call her Warc.
I think I got it all down for you and put some pieces to the puzzle together, but my explanation could have been a bit stronger if I had any knowledge of the actual story before the fighting games.
In my opinion, Bousou Arc sounds nice too. Whatever floats your boat.