technically, the title of "first lady" never existed in the UAE
during the ruling of Sheikh Zayed, Fatima was mentioned like this:
"H.H. Sheikha Fatima Bint Mubarak, President's wife and Chairwoman of the UAE Women's Federation"
since Sheikh Zayed's death, she is mentioned like this:
"H.H. Sheikha Fatima bint Mubarak, Chairwoman of the General Women's Union (GWU), President of the Supreme Council for Motherhood and Childhood, and Supreme Chairwoman of the Family Development Foundation (FDF)."
Sheikha Hessa bint Mohamed never received any public mentions before her death. In the news of her death, she was mentioned this way:
"Sheikha Hessa bint Mohammed bin Khalifa Al Nahyan, the mother of President His Highness Sheikh Khalifa bin Zayed Al Nahyan"
Official media knows that Hessa was Zayed's wife, then why wouldn't mention it. Yes, sometimes they dont add wife of this Sheikh, this is because of their lack of information. I still believe that media doesn't know which daughter of Tahnoon bin Mohammed married to whom even though they know Mouza and Salama bint Tahnoon very well.