I don't mind the bitchy (hell, I agree, she should be even more badass), but I mind the bitchy immaturity. Under Sturges, she's so mean to Paco in such a totally childish way (deflecting and avoiding the subject like a damn 12-year-old when he was trying to ask her out, laughing at him when he said he loved her), which is, imo, so wrong for Brenda. She's smart and mature and if she flies off the handle a little, that's not a bad thing. She's had a hard life. She's allowed to be angry (and frankly, I love her all the more for it).
Also, it makes it seem with the crying and such that Sturges is saying that Brenda's anger and bitchiness is just masking her ~true feelings~, and she needs to stop being that way and start being nice and loving in order to be happy and live a full life and blah blah blah, which I am not so down with. I want my smart, bitchy Brenda, dammit!