I don't know how old your mom is, but my pet theory of authority is that people older than about 40 accept printed text as authoritative. As in, non-handwritten letters that look regular.

When we were kids, you had either direct speech, hand-written words, or printed words.

The first two could be done by anybody. Anything informal like your local message board would be handwritten, sometimes with crappy printing from a home printer. It used to cost a bit to print text that looked nice, and that text used to be associated with a book or newspaper, which were authoritative.

Now suddenly everything you read is shaped like a newspaper. There's even crappy news websites that have the physical appearance of a proper newspaper website, with misinformation on them.