I also think that Gisela and Marie Valérie had a good relationship. When Valérie was still unmarried, Gisela and her family often went to Vienna or Bad Ischl where they stayed for more than two months. Above all, Gisela loved to stay at the Hermesvilla (which was built for Empress Elisabeth, but unfortunately she didn't like it) where some rooms where named after her.
I don't think that Marie Valérie visited Bavaria very often, but nevertheless the sisters were in contact. They met at different family celebrations, health resorts and again and again in the area around Vienna as both of the girls loved their father Franz Joseph so much.
It seems like Franz Joseph, Elisabeth and their daughters shared their letters all the time. In FJ's letters you can usually read "I sent you Gisela's letter ..." or "I don't know if you have heard from Valérie so far, so here is her letter ...", etc. So everyone got the latest news from the other family members. That's really nice.