Yes,it came out, as you said, in another thread, and it is true, they hated each other.
I have no documentation at hand so I may be wrong, but I think Marķa Luisa and Marķa Carolina never met each other. Marķa Luisa lived in Spain between 1765 and 1808. She never traveled to other country in those years, not until she went to Bayonne with the rest of the Royal Family.
And until 1765 Marķa Carolina hadn't yet set foot out of Austria. Marķa Luisa lived in France during the Spanish War of Independence (1808-1813) and then moved to Italy. Carlos IV and Marķa Luisa spent much time in Naples with Carlos's brother King Ferdinando and all of his family (in which Marķa Isabel was included). But this was not until 1816, when Ferdinando regained the throne as Ferdinando I of the Two Sicilies. By then Marķa Carolina had been dead and buried for two years. So I don't think they ever met in person.
However Marķa Luisa also disliked Ferdinando! And he hated her also! What a loving family picture!