The Lost Pines Resort is beautiful, but it is VERY EXPENSIVE to stay there. It is about 15-20 miles west of the airport, and there aren't many other lodging options outside of heading back into Austin.
If Austin is the chosen location, I'd suggest approaching LifeTime Fitness to host the event. If it's an outdoor event, Austin of course has many gorgeous locations (many of which are free but probably not for an event of this size), but Zilker Park would be the most well known and provide a gorgeous view of downtown.
I don't think you can go wrong with Austin, Dallas, or Houston - the larger Texas cities.
Please keep us posted! I live in Austin but would travel to any of the large cities for the chance to see Cathe again!!
Thanks,
FitGirl-ATX