On pg.14 Ms. Smith says that vampires not showing up in mirrors is totally fictitious, but that might not necessarily be true. Most modern mirrors use aluminum, tin, or just glass as the reflective property, but older mirrors (or ridiculously expensive modern mirrors) use silver. Which as Ms. Smith points out on the next page, silver is one of the weaknesses of vampires. Meaning it's entirely possible that vampires wouldn't be able to see themselves in a silver mirror, but given how expensive they are now that wouldn't be an issue unless you're insanely rich.