Horseshoe Meadows is the trailhead for both the Cottonwood Lakes trail and the Cottonwood Pass trail. Either make a nice warm-up hike for Whitney. Neither are very strenuous, and Cottonwood Pass is close to 12K'. If you're feeling adventurous, the Cottonwood Lakes trail will take you to Army and New Army passes, as well as to Mt. Langley. That would be overkill though - you don't want to burn out on gain right before your second shot at Whitney.
No matter which trail you take, be prepared to slog through some beach sand at the outset. A real PITA the first mile heading up to the lakes.
Good luck with round two!
