Why are some people so rude?

Maybe it's just me, but I really don't get it... There's this friend, lets call her Jane. There have been a number of incidents in the past between her and others I know. I've tried defending her, and giving her the benefit of the doubt time and again. I've been nothing but nice, honestly.

Recently, she got into an online argument with someone very close, and said some VERY rude things that are directly related to myself and my family. "Jane" is taking issue with a very petty thing, and blowing it way out of proportion, and in the process, was very insulting.

Insulted person believes I shouldn't say anything, and we should just comply with what "Jane" wants... Sorry, but no! I do NOT take kindly to people offending my family, and I will NOT just sit down and let her trample all over said close friends while I stick up for her.

Sorry, but I am DONE! Ugh... I really hate people like that. :(