Here is a description of Sisi's relationship with Valerie from Clara Tschudi's biography of the Empress:
The year following the coronation in Hungary, and ten years after the birth of the Crown Prince, a little girl was born, the Archduchess Marie Valerie, in the royal castle at Buda, April 22nd, 1868.
The joyful event was announced to the populace by the firing of cannon from every fortress at six o'clock in the morning. It was the first time for a century that a royal child had been born in Hungary, and the delight of the Magyars was unbounded. As night approached, the whole city was illuminated, and crowds filled the streets, hundreds of them on their way to the castle to send up a ceaseless cheer and "eljen" for the King, for the new-born Princess, but especially for the Queen.
Valerie was the youngest and most cherished of Elizabeth's children, not that she did not love Gisela and Rudolph, but her mother-in-law, aided by governesses and tutors, had alienated them from her, and she had not been serious enough in her efforts to have them with her. Her maternal devotion had been lacking in the firmness and quiet self-sacrifice that would have commanded respect for her rights as a mother, and this had led her to relinquish all, and forsake her children.
But this time her motherly love was there in all its intensity, and the recollection of past sorrow was obliterated by the unspeakable tenderness she felt for the fragile little being that nestled in her arms, and from the moment of the child's birth she resolved to superintend her bringing up and development herself.
The Hungarian author, Maurus Jokai relates the following incident:—
"In 1869 the Queen most kindly allowed me to dedicate one of my novels to her, and as the Royal Court was at that time in Buda, I was able to present a copy to her in person, and to enjoy a long detailed conversation on the literature of Hungary. As I was on the point of leaving, she said: 'Wait a moment! I will show you my daughter.'
She opened a side door and signed to a nurse, who brought the child into the room. The Queen took the little one in her arms and pressed her to her heart; I shall never forget the pretty sight."
Marie Valerie was very delicate as a child, and her mother was the first by her bedside in the morning, even after listening at the door more than once in the night to ascertain if she was asleep; and if the little one was ill her mother refused to leave her, and could with difficulty be persuaded to take needful rest."
She recognised with contrition that in consequence of the disagreement with her husband, she had neglected her children, and she was resolved to atone for her mistake as far as possible.Even as Valerie has often been neglected in favor of her beautiful, troubled mother or her notorious, tragic brother, so Elisabeth's personal eccentricities and marital and familial problems have been emphasized at the expense of her more positive relationship with Valerie. It is fair to note that the very intensity of her mother's affection, arousing the envy of siblings and the criticism of courtiers, caused Valerie some pain and embarrassment. Nevertheless, Elisabeth's devotion to her youngest daughter suggests a depth of love and generosity perhaps too easily forgotten.