The two would most likely fear each other at first due to Mavis being a vampire and Elsa's ice and snow powers. But overtime, the girls would learn to get along. Both Mavis and Elsa were isolated by their parents. Their parents were overprotective and kept them sheltered for a long time. Mavis reminds Elsa of her younger sister, Anna, who has the same personality. They won't get along at first but eventually, they'll learn from each other.
Some fans picture them as friends while others see them as a romantic pairing.