The age of mirror-bearing DSLR's is over, so no problem in that regard. And it seems like she can show up in mirrors if she's focusing on hiding her vampire presence. She started fading when thinking about the sister's question, so appearing in mirrors is probably some kind of concentration spell.
overall strange how they otherwise don't react to the clearly different EARS. Even the little brother was unfazed (but the men some chapters ago did react thinking they were cosplay)