I cut her some slack on the Soames front, because he's clearly kind of a lunatic, and she did warn him that she might end up hating him and want to leave. It's a weasel's move, but you could argue that her mother forced her into the marriage.
However, here is the rest of her track record:
1. Break up your best friend's engagement (meanwhile cheating on your husband).
2. Drive the ex-fiancé to suicide.
3. Take up with husband's cousin, thus forcing the divorce.
4. Raise a milquetoast mama's boy.
5. Manipulate the mama's boy into not marrying the woman he loves by invoking the memory of his dead father in a particularly repellent way.
The whole time, everyone (except Soames) just lets her get away with everything, because of her compelling beauty. Even though she's a truly terrible person. And not only is she terrible, but she refuses to take any responsibility for any of her destructive and cruel actions. Never was anyone less aptly named. Your irony is staggering, Mr. Galsworthy.