I love Scarlett and Imogen but my vote goes to Imogen (one of my DH's faves too) because Scarlett Fox sounds like you are describing something.
Good luck!!
Congrats on your pretty little baby! Looks like a gorgeous "Ava" to me! This would be my first choice as her first name, out of your choices!
You can go with a longer version (Avianna, Giavana, Aviana, Avery) and call her Ava for short??
Ava Imogen Fox
Avery Imogen Fox
Avianna Imogen Fox
Giavana Imogen Fox
Just a thought!