She was a very religious woman and was noted as having a cold personality as well as being very shy.
She sounds like her elder sister the Dauphine Maria Teresa Rafaela, who was also considered to be shy, cold and religious - and consequently not very popular at the French court, except with her husband. Her identification with the Dauphin's interests, and the dislike the Dauphin had towards Madame de Pompadour, probably had more to do with the decision not to have another Spanish princess as Dauphine - Madame de Pompadour sponsored a Saxon princess instead, from the family of her friend the Marechal de Saxe, who she thought was more likely to be grateful to her patroness and behave graciously towards her.