I'm not too fond of
Savannah, but I can understand it's appeal. And
Georgia is the first thing I think of when I hear
Savannah, but that's far from a bad thing. :) It's definitely a lovely, very refined, old city, so a
Savannah would have a great association with her name.
As for the nickname
Izzy for
Tristan, I'm going to say no for two reasons: 1) I'm of the opinion that
Tristan is a male name and even if you were using
Tristan for a male, the nickname
Izzy is too feminine. 2) The nickname
Izzy is too reminiscent of the
Tristan and
Isolde mythology. To me, it would be like naming your child
Juliet, but calling her
Romy (reminiscent of
Romeo).
_____