To make the leap that my being concerned with inappropriate conduct directed to my niece implies a weird relationship is nonsense.

First off, she is three time zones away. Second, I got the information from my sister (her mom). Third, I never would contemplate physically confronting children (or adults, except in very extreme circumstances) frankly. All I ever contemplated was a one-page letter. Over the top? Yes. But whatever you are imagining is ridiculous.