Meaning of "full of it"

The full text of the paragraph identifies the antecedent:

Immersed in all this, and aware that her post-war work had been secret, she never mentioned her constitution-drafting until 1995, when she wrote a memoir. After that, she was full of it. Yet, when all was said and done, she did not think Article 24 was the most important clause in Japan’s post-war constitution. That honour, she said, belonged to Article 9, under which Japan renounced war and embraced peace. And hers was second.

Initially, she was silent on her role in drafting Japan's constitution. Her life lacked any mention of this contribution. In 1995, she wrote a memoir. Following that, her conversation would regularly include references to "it," meaning her contributions.

Agreed, the text is not great - I'm assuming an earlier draft of the obituary had a more directly stated antecedent - but it is still discernible from context. Indeed, absent a clear antecedent, it does seem like she was full of crap, but the rest of the article doesn't really fit if that's the case.

It would be necessary to read the article in full to be sure, but it probably means that she never stopped talking about it.

Full of it here doesn’t necessarily mean full of shit or talking rubbish.

Full of it can also refer to someone who talks themselves up or try and make out they’re far more important than they actually are. In other words full of themselves or full of their own self importance and to support that will go on and on about their one main achievement in life, here the Article 24.

It’s mostly coloquial, used in everyday speech.

There are relevant dictionary entries:

full (9) (postpositive; foll by of) occupied or engrossed (with) full of his own projects

Collins English Dictionary – Complete and Unabridged © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003

(also at AHDEL)