Wow, thank you all for such good advice...
I think Palm Springs and Santa Barbara are out - my friend wants it to be something that she wouldn't normally do on a long weekend. And while I love the idea of Vancouver or Whistler, she's originally from the northwest so it doesn't seem exotic enough to her.
We're now discussing a 7-night Mexican cruise from LA, a shorter Caribbean cruise from Florida or San Juan, or a yoga retreat somewhere in Latin America. I know that this is flyertalk, but the idea of taking a weeklong vacation without having to get on a plane is very appealing. That said, the Caribbean destinations seem more interesting (opportunities to visit Mayan ruins or hike to old battlements).
Please feel free to keep offering advice because I never would have imagined that planning a vacation without a set desination could be this difficult!