Repented? There's no repentance. She didn't do anything wrong.
Arwen was half-elf (like her father, uncle, and brothers). They were given a choice - to be mortal or immortal. Arwen had until her father left Middle-earth to decide. She made her choice, and it was undoubtedly permanent.
What's the half-elven choice all about? Here's an article and a link to other threads on the same subject.