Actually, this isn't strictly impossible:
Vampires aren't reflected in mirrors because silver is said to repel evil, and old mirrors of course are mostly made of silver.

It isn't unthinkable that Remilia had a mirror made with some other metal so she could use it.

Or, you know, magic.

Or, you know, she doesn't follow that rule either?

I quite like shiftc's explanation. So that's how it works.

Well, another possibility is that it's not Remilia who's looking into the mirror. Magic.

I guess the mirror is made from chrome these days...

Or it could be a portrait.

6163 said:
Or it could be a portrait.

Yeah except aren't vampires not supposed to show up on film either?

After the 19th century when camera is invented.
Vampires can still be portraited through the hand of artists.

The surface texture doesn’t look like a metal mirror.

Fallenangel407 said:
Yeah except aren't vampires not supposed to show up on film either?

As in a painting.

Amraphenson said:
As in a painting.

Oh geez! I misread portrait as picture!

Or it could be a window.

Looks like a small framed photo on a table next to a glass of wine if you ask me.

It's actually a window and she's sitting behind it. That's my story and I'm sticking to it.

[deleted]

Pixiv title confirms it's a portrait. Removing from "How is that even possible?" pool.