I have yet to find any law - and certainly any Constitutional provision - that says a person can be compelled to make statements incriminating themselves, "under certain conditions".
She can answer fifteen questions from Issa if she wants, and then if she feels the sixteenth question might incriminate her, she can plead the 5th on that question. Then answer three more, then plead the 5th on the next six, etc. etc.
Where in the Constitution does it say that if you answer one question, you must answer them all? It says pretty much the opposite if you ask me.
Or does it say that right after the section that says government can make 'reasonable restrictions" to your right to keep and bear arms?
However, if Congress grants her immunity from prosecution, then she cannot possibly make self-incriminating statements... so THEN she can be compelled to answer, on pain of getting tossed in the hoosegow for contempt of Congress if she doesn't.