I think the problem of Cristina has always been the same, she is very proud and selfish. For years she was the nice girl with perfect and simple family, as opposed to Elena ... but her life was not really so "humble" and she enjoyed much of her privileges. Royal yacht, skiing, parties of royalty ... she took advantage of all.
Infantas Elena and Cristina were educated, or should have been educated, knowing that in the future their role would be secondary. With the arrival of the Princess of Asturias, she would be above them, and inevitably would have to have a more important role.
I always thought that the reason they have imposed a restrictive role as minimal for Letizia, was by jealousy of other ladies of the family. The Queen's office also carries the affairs of the infantas.... Princess Letizia depends on the Prince´s office ... so always had to have major "battles" for power in Zarzuela.
I think Cristina, by her nature, is who has had some power over her brother and sister ... she tried to have it on Letizia, and could not.
We must remember that the engagement ring of Letizia was the same model as Cristina, in the engagement Letizia wore a Armani suit (and received much criticism for wearing a foreign designer), as Cristina wore in hers... It was obvious that what worked for a infanta would not work for the new princess ... Letizia understood it, I do not think Cristina.
The press has always been busy blaming Letizia all, it was the easiest. But rarely analyze the personality and attitude of other members of the Royal Family, and how a new person coming from outside, could fit into all that.