Options...
Apple TV can work with or without a TV and you can choose between hdmi and optical. If there's a TV connected to her stereo, then to me there's no other option for the money. ($99 for ATV then $40 of monoprice optical dac (disable dolby-digital, i.e. pcm only)). Configuration is rather simple with a TV with the included IR remote.
Airport express, as already noted, but use the mini-Toslink optical output over the minijack. For whatever reason the optical output does a bit of buffering where the analog output doesn't. You can pick up a reasonable mid-fi dac on monoprice. How you connect the airport express to the Verizon router is important to understand:
Wired connection: should be easy to configure with the AirPort Utility
Wireless connection: you need to connect initially to the router to configure, and you need extend the Verizon router's wireless network (vs router/bridge mode).
Use an existing gaming console, blu-ray player and even a TV that has uPNP and install one of the many applications on her mac. Some might consider it difficult to integrate with itunes.
Sonos is another option, but priced a bit more but has a better internet radio interface than the Apple TV.
If she has an iphone or ipod touch, they make for great remotes to control and build a playlist otherwise use the IR remote for the macbook pro, which will help skip a track. There's apps to control all the above.
