She isn't a housewife as Sarah said.
We're waiting for the "Why" as well. Hopefully they'll feed us a bit of new information soon.

She would have almost undoubtedly had a career practicing law before becoming a law professor, and as IMW said, could have been a prosecutor. Though even as a defense attorney she could have come up against someone who would want retribution for something. I don't know why I lean toward her having practiced criminal law but I do. Granted she could have taught a subject for which practical experience would not be required, but all of my professors in law school had practiced (and some still practiced) law at some point before becoming professors.

Jack Skellington said:

Rewatching the episode last night, Beckett says that her mom was putting together an appeal for Pulgatti.  We know that Raglan and the other two clowns killed the FBI agent and Pulgatti took the fall.  If Pulgatti told her about this in his letter to her (prompting her appeal) then Johanna and everyone working with her on the appeal (law clerk etc) knew all about the real way it went down.

 

Raglan and the other two most likely didnt come up with the kidnapping idea themselves.  So busting them would expose "the dragon".  By Killing Johanna and the other 3 working on her, the only person willing to help Pulgatti is out of the picture.

 

Bottom line, I think we already know why she was killed in its simplest sense.  Who ordered it and why they didnt want the conspiracy outed, I think is really what Beckett is after now.