First of all, buy her that iPhone. Now that Verizon is a player as well as AT&T, chances are better that you can swing an iPhone purchase plus talk/data plan with an acceptable carrier. The iPhone is practically the perfect Mommy comm unit.
Gone are the Crackberry days of yore. Today's mom wants to talk, shop, surf and game as well as email. Plus, you can comfortably give your iPhone to a 4-year-old with the expectation that the child will be able to navigate the system, amuse himself or herself and get the phone back in reasonable condition without destroying or messing with your stuff -- not something that the BlackBerry was ever much good for.
Next, buy her some awesome navigation software. We've got Mel Martin's overview of the offerings out there. We moms spend so much time in our minivans (and SUVs and econocars and leafygreens) driving your kids from point A to activity B -- every little bit helps.
Navigation apps are costly enough that a lot of moms don't spring for them for themselves. So buy one for her -- add in a dashmount kit, too, so she's not holding the phone in one hand while she navigates (Mike Rose recommends the Arkon IPM512, but there are scores of models to choose from). You might also want to throw in a car charger, to make sure that her iPhone remains charged while directing her to all her unique and special destinations. Like 10 doctors appointments, the cabinet refinishers and the dog groomers.
Think about some great apps for walking and running. We moms need time to ourselves. Although I am personally a RunMeter addict, there are any number of other terrific exercise-promoting apps, many of which will provide live tracking so that you can drive up to her, as she's finally ALONE by HERSELF and AWAY FROM THE KIDS, with your beloved junior family member howling in the back seat having skinned his knee, and acting inconsolable for Mom, when a simple Band-Aid and spray antibiotic, not to mention a kiss on the booboo could be administered by the most loving partner by him or herself.
Not that that ever happened. That was totally a theoretical example.
On second thought, you might want to disable the tracking feature for your beloved, even as you allow her to find her inner peace and regain her groove with a little exercise on her own. She could, however, use Glympse to allow you to see how far along the day's journey she might be at a particular moment -- even better, you could install it yourself to let her know exactly when you're getting home.
Think about a photography app to help her convey the true experience of her Mom time. We're fans of the clever and speedy Camera Plus Pro (demoed here) for stills/video and the impressive You Gotta See This! and 360 Panorama for full-circle images; readers also recommend Superama.
Finally, consider buying a really big iTunes gift card and letting her choose some amazing applications (not to mention tunes) that she's been wanting but hasn't gotten around to buying.
Sometimes you just gotta let The Essential Barry Manilow or a little bit of Katy Perry or Justin Bieber, sneak onto an iPhone without anyone knowing. And a gift card can provide that kind of discrete "Ripple-in-the-Paper-Bag" style cover you need.