Hi Aaron,
This may seem obvious, but have you and your wife considered the Poseidon Odin? The Odin sounds ideal for your wife, given your 'criteria':
1) it's world famous for handling low temperatures.
2) it's also world famous for supplying plenty of air at any depth.......the Odin has a 'servo-assisted' 2nd stage, which is great for providing a satisfying 'woosh' of air when your wife inhales......very relaxing to breathe. Also, take a look at the 2nd-stage orfice where the mouthpiece joins the 2nd-stage body, you will see that the air opening has probably twice the cross-sectional area to inhale and exhale air through of a 'typical' regulator.....another tribute to the Odin design where maximum air flow is a top priority.
3) it would be ideal for your wife's interest in photography.....the side-exhaust for exhaled bubbles in the Odin is unsurpassed for clear, unobstructed vision......vastly superior to a 'conventional' reg such as SP or Apeks,.....
I'd encourage your wife to test dive the Odin to actually experience the clarity of UW vision....she will totally forget she is even exhaling.....she might hear the bubbles, but she certainly won't see them.
4) jaw fatigue is a non-issue, especially since Poseidon recently started to equip all it's regs with a new generation of soft-silicone mouthpieces......very comfortable, and last fall I switched out the original mouthpieces on my 3 Odin reg sets to these 'new' mouthpieces and have been tremendously pleased with the comfort.
If you lived in the Dallas/Ft Worth Tx area I'd be happy to loan your wife an Odin to test dive......but even if that's impossible, I'd encourage your wife to find a friend or dive shop where she could test dive the Odin before making her final decision......I think it would be exactly what she's looking for!
Karl