A flash of recognition for the surname-- Wanda Maximoff, so that explains why he looks familiar, because he's part of their family. The cheekbnes and the jawline remind her of Erik, she realizes, which is why she says: "Rheintochter," mimicking the way he pronounces it. "Rhinemaiden. Mermaids are from the sea."

Salt water does nothing for her and she's not over-fond of the ocean in general, it being a place where she's much lower on the supernatural foodchain than she is in her river. She can't be blamed for preferring her own territory.