But I digress. I'd be interested in seeing Teri's Adidas shoes to get a sense of the wear pattern. Overall, I'd say four months of use sounds about right for someone training for a marathon and probably running 50 to 60 miles a week. But often a shoe at that point can still look pretty good—it's the cushioning that's shot. So signs of unusual wear can tell you a lot. That said, you seem to have a good sense of her running style: she's a forefoot striker, has some stability problems, and, as an aside, has generally pretty rotten feet.
So what shoes are best? One good candidate: the Brooks Ariel ($110; www.brooksrunning.com). This shoe is designed for a runner such as Teri, who has flattish feet and some stability issues. It's always tough to mix stability with cushioning, but the Ariel has Brooks' HydroFlow chambers in both the heel and forefoot. If Teri is a pronator—and most runners with stability issues are—then the Asics Gel-Foundation Plus ($90; www.asics.com) is another good shoe; very stable, with pretty good cushioning. The New Balance 900 ($100; www.newbalance.com) offers neutral stability and decent cushioning in a great shoe for a high-mileage runner.
In any shoe, Teri might benefit from a pair of Superfeet ($28-$35; www.rei.com), after-market insoles that add stability and cushioning to any shoe. They might help.
I hope your sis has fun and doesn't ditch the sport in a huff like me!
For the year's best running shoes, read the reviews from Outside's 2004 Buyer's Guide.