Why is Eir named “Eir Stegalkin” and not “Eir Einarsdottir” (after her father Einar Cliffstrider)?
I thought, Norn use the names of their (famous) ancestors.
From the Wiki
Most norn follow a Northern European or Viking-style first name system, though some like the famous explorer Captain Romke and his crew have Dutch and Frisian names.
Their surnames can vary in a multitude of styles. Norn without any achievements or legends have surnames after one of their parents (father/mother's first name followed by -sson or -sdottir or a variant thereof); this is most commonly seen in children, and they're named after the more famous of their parents even if they do not like said parent (e.g., Braham Eirsson). Surnames do not get adopted from generation to generation and they can be changed by the individual to fit their own personal legend (e.g., a famous Wolfborn member took the surname Wolfsdottir); married couples may not always share surnames either (though some may, e.g., Knut and Gaerta Whitebear). Some norn may also take titles instead of a surname if it fits them and their legend more (e.g., Borje the Sun Chaser).
Basically they do what they please based on vague guidelines. If they take it from direct family, they may start with the more famous parent then change it later in adulthood
To my knowledge, "Stegalkin" has never been clarified as a reference
Here's a discussion from the old forums I found for you https://forum-en.gw2archive.eu/forum/game/lore/Eir-s-last-name