What is "it" in this statement?

Question

In the case of "She's not joking. She's saying it seriously.", what is "it"? Where is the idea that "it" is replacing? "She's saying she's not joking seriously"? Or is it "She's saying it's not a joke, seriously"?

I understand that I have to use "le" here as the lesson is about replacing an idea, but the idea seems so disconnected that I can't nail down what "le" represents, or why "en" would not be just as valid.

Accepted Answer

Hi Gilbert,
Here the 'it' is vague just as 'le' in French.
Without the full context, it is impossible to know what has been said but in my opinion, it is a literal translation of the situation in English. 
Elle ne plaisante pas, elle le dit sérieusement = She is not joking she is saying it ( whatever it is ) seriously 
A fuller context could be -
Quand elle dit qu'elle t'aime, elle ne plaisante pas, elle le dit sérieusement = When she says she is in love with you, she is not joking, she means it
Hope this helps!

Answer

I now get why "en" would not be valid, but I still don't quite get what the idea, opinion or statement is that "le" is replacing in this example.  Might be a good example to mention in the lesson? (Sorry, this is the TEFL teacher coming out in me)

Answer

If someone says, "She is not joking. She is saying it seriously," this clearly refers to something that was said previously. You could ask, what she was serious about. The answer to that question is what "it" (or the French le) refers to.

Answer

This is as simple as ‘it’ is whatever ‘it’ is that she is not joking about - and she is actually serious about ‘it’. Clearly, as Çecile notes, this is a fragment of a conversation, not completely bound statements, and represents very natural and normal speech in either English or French, and presumably many other languages too.