A fitness tip for a short term goal: LUNGES!
Those old fashioned, long strides that leaves you almost touching your back knee to the ground, whilst the front knee is bent. Begin these immediately -- adding more each session of everyother day. When I decided to do Whitney, I had not done any hiking that season -- about 2 1/2 weeks before the trip -- and my only fitness base was running. Running alone will not build the quad/knee strength/endurance that is required for elevation gain hikes like HD and Whitney. The lunges are the quickest way to acquire and add the muscles needed in such a short time (I breezed up the switchbacks with nary an ache)
Speaking of ache: there is no comparable ache to that of a pounding, steep downhill, so I vote for JMT, also.
Bee kind and understanding with your fiance, as she is to be your lifetime partner (who may save your butt someday)
