Hmm..... TBH I don't think Eternity goes with Zara (probably wouldn't go with many names). Is there a variation for Eternity that your DH might go for or perhaps an alternative. I know my DH threw up the name Trinity. I like but don't love it IYKWIM.... If you were to consider Eternity I'd put in the second middle name of Elizabeth and go with Zara Elizabeth Eternity - flows the best I think. JMO of course!