No trail "intersects" Sweat Heifer between its two ends (the AT and Kephart Shelter).
A hike to Abram's would have been my first suggestion if she wanted to see water falls... it's my personal favorite in the park.
If you want unusual views (i.e. something besides Clingman's Dome that EVERYONE goes to) and insist on doing a portion of the AT, you might want to consider driving out to Fontana Dam. The dam itself makes for an interesting trip... and if the road over the dam isn't closed, its less than 3.5 miles to the Shuck Stack fire tower (however, it's about a 2,500' elevation change in that 3.5 miles).