Zarzuela could say 'no' if they wanted to, I'm pretty sure they had said 'no' many times over the last 10 years since I doubt that was the first invitation Letizia received. The last 10 years, Zarzuela denied Letizia a more visible role, at the same time let the media blame her lacking of a role on herself, how convenient !
. Since the VF article last Dec, media has started to talk about Zarzuela purposely leaving her in the shadow, although still mild, but can get heated up in the future. I'm sure Zarzuela has been taking a note on all the subjects since JC today can't 'afford' to do whatever he wants as before.
