Fifth Amendment question

Help me out here, folks - I'm not asking for anyone's partisan political opinion, so please, please, please don't give one - So, Lois Lerner, formerly of the IRS, has been found in contempt of Congress by the House of Representatives for invoking her Fifth Amendment right not to incriminate herself by answering questions during their hearings.

http://www.washingtonpost.com/blogs/post-politics/wp/2014/05/07/house-votes-to-hold-lois-lerner-in-contempt-of-congress/

I watched some of the Congressional hearings, and the bloviating Congressmen (of both parties) went after her with gusto.  Love to watch them posture, by the way.  It's great theater.

Here is a Wikipedia* explanation of the portion of the Fifth Amendment that deals with protection against self incrimination:

"The privilege against compelled self-incrimination is defined as "the constitutional right of a person to refuse to answer questions or otherwise give testimony against himself or herself. ... "^[34]To "plead the Fifth" is to refuse to answer any question because "the implications of the question, in the setting in which it is asked" lead a claimant to possess a "reasonable cause to apprehend danger from a direct answer", believing that "a responsive answer to the question or an explanation of why it cannot be answered might be dangerous because injurious disclosure could result."

(http://en.wikipedia.org/wiki/Fifth_Amendment_to_the_United_States_Constitution)

[Oh, by the way, I'm a CPA and I deal with the IRS all the time - there are a lot of good folks who work for them, but I also think that as an organization they have a lot of meanness inside (they need a good hug, is what I say)]

 I'm in no way defending what Ms. Lerner or the IRS may, or may not have done.  I'm talking about Congress apparently feeling that she should not be afforded Constitutional protection when it doesn't suit them.

Anyhow - here is my question:  Why is she being held in contempt of Congress? I mean, what is the legal justification for that charge?

I was at the Post Office the other day - you know, that place where you send messages that are written on pieces of paper, instead of sent electronically - and a guy was at the counter, talking about the whole situation.  He said "they ought to arrest her for taking the Fifth".

Do we now pick and choose when to follow the Constitution? Does our Constitution only apply to those we like?

*It's on the internet, AND on Wikipedia, so it must be correct, right?**

**That was snark, in case you didn't catch it.