Brenda Walsh was NOT a bitch or a cruel person in any respect. She was a 16 year old girl, who found her first true love and then lost that love due to the betrayal of her so-called closest friend. It's a simple case of "imagine if it were you." In your pain and anger would you not lash out at people after being let down by those you trusted?
Brenda was - by far - the best character in the show. She was intelligent, witty, funny, honest and kind. Her stuck up friends - all of whom were obsessed with being adults instead of simply enjoying the freedom of being teenagers - were the bitchy ones. The media is full of s**t; they spin little things into webs of deceit, it's just what they do. And that is exactly what they did to Brenda/Shannen during the 90210 days.