A lot of people in the comments are saying that it's Carol. Which I 100% deny.

Look at the color schemes. Blue and pink. Girlfriend's eyes represented with an orange color. This is very obviously B-SIDES WHITTY.

Blue and pink color schemes are everywhere in B-Sides. In the teasers, on the main menu screen. Heck, even Boyfriend's blue hair color is changed to pink in B-Sides!

Now, you might be asking "But what about the orange Girlfriend eyes?"

Well...

What color is Girlfriend's hair in the B-Sides mod?

It's an orange-ish yellow.

I have more proof to sustain this theory. First, Rozebud, the creator of B-Sides, worked on Whitty, and in an interview with YouTuber and Twitch Streamer UniqueGeese, he said that he's "just here", meaning he didn't work on Whitty. This implies that he was there because he's working on B-Sides Whitty.

Second, in the same interview, Rozebud showed a clip of what seems to be a Ballistic remix. I don't think I have to explain anything else after this point.

So, yeah, it's very clearly B-Sides Whitty.