There are a few informations on Marie- VAlérie in the Brigitte Hamann's book.
Marie Valérie was very very shy.. She called this deep shyness "my génation" (sorry I can't traduce in english, but it means that this shyness was a big trouble for her).. When she was toddler, Her mother's ladies in honor didn't like her, because like all shy people, she seemed haughty and distant. She was said to be "strange". And the fact that she was the "kedvesem", the dear daughter of the hatred Sissi, didn't arrange things.
I find that Marie-valérie looked like her father very much. They had also identical conceptions. The difference was that Marie-Valérie was not really Habsburg by heart. Of course, she loved her country, her family and its high position, but she would dream of a huge German Community which would have included Habsburg ,Hollenzollern and all the german blood people. In this point of view, she was different of her family and of the court which had anti-germanic feelings.
After her mother's death, she seemed to have had very hard feelings for her family, except for her father of course(maybe a disgut of court life I don't know). At the beginning of the 20th century, She wrote in her diary that she wanted her children to grow up far away from this court and this family. She spend the rest of her life in a real isolation in her Wallee castle, leaving it only for the wedding of Charles I and Zita, or to close her father's eyes.