And she has every right to be.
That everyone questions it. That Bianca questions it. That is just wrong. Like an old Jeff Foxworthy routine twisted just a bit: You might be a misogynist asshole if you think Kat Stratford is wrong for being a bitch. You might be a misogynist asshole if you think Kat isn't justified in getting mad at Patrick for hiding the fact that Joey's paying him. And You might be a misogynist asshole, or just fundamentally misunderstand feminism, if you can't accept that Kat can turn right around and forgive him because (whether it's just a teenage version, or cinematic teenage version, or something more real) she loves him.
Plus, even if she’s compromising her beliefs, she’s doing it for Heath Ledger. Who wouldn’t do that?