Driver software for Kensington Turbo Mouse Pro on 10.7
Your wife has excellent taste in input devices. I use the same trackball daily, and if I can't also find a solid Lion solution, I'll be heartbroken (not to mention much less productive).

History:



Kensington shipped four models of this type. The Expert and Turbo versions had slightly different coloring, and each came in wired and wireless versions.


K64213 Expert Mouse Pro 
K64214 Turbo Mouse Pro
K64245 Expert Mouse Pro Wireless
K64240 Turbo Mouse Pro Wireless


The good news:

According to Kensington's drivers page, TrackballWorks™ 1.1 for Mac was released on Oct 19, 2011.

[Note: yes, that's TrackballWorks, not MouseWorks—the latter was last updated in 2009.] 

The Installation/Notes file says:


  Requirements:
  Apple OSX 10.5.6 Leopard
  Apple OSX 10.6.x Snow Leopard
  Apple OSX 10.7.x Lion  
  
  Description: Enables trackball customization: button functions, pointer speed and acceleration, and scrolling speed and direction.  
  
  Languages: English  
  
  Installation:
  Save the DMG file to your desktop and double-click on it.
  Click on the installer package icon when it appears.
  Follow the on-screen instructions to install the software.


The bad news:

I haven't been able to get it to work, and I'm not the only one.

Kensington support says: 


  TrackballWorks - Supported Kensington Devices
  
  Which Kensington trackball models are compatible with the software application TrackballWorks?
  
  Kensington TrackballWorks is compatible with SlimBlade TrackBall model K72327, Expert Mouse model K64325, Orbit Trackball w/Scroll Ring model 72337, and Orbit Optical Trackball K64327.


Note that all the supported models have numbers greater than K642nn.

Workarounds?


There are some reports of success with TrackballWorks, so it's worth a try.
There are third-party mouse drivers. Some people have switched over to using USB Overdrive. I'm currently trying out SteerMouse, which makes the trackball work, but only has limited button support.

Neither focuses on supporting Kensington devices, or trackballs in general, which makes things problematic.