This is a sticky situation but I definitely don't think Tiffany is a real friend.

I came from a conservative small southern town and half of my family is very closed minded. I'm now the heathen aunt that lives in California. And as the heathen aunt, I post all kinds of things to social media that I'm sure pisses of my family, but I don't dare get into those topics when I'm around them. So I sort of get where Tiffany is coming from in that regard. If I were Tiffany in this situation, I probably wouldn't have said anything, let mom say whatever bigoted shit she wanted to say in order to avoid an argument, then checked in with you later to apologize and explain why I couldn't say anything in the moment, etc.

HOWEVER, I absolutely would NOT hound a friend about buying a gift that ruffled my mother's feathers. Should you have waited to give the book to her in private when she wasn't around her family? Maybe. But do I think she's justified in chastising you about your gift? Absolutely not. She could have just sent a thank you card and moved on.