The analogy I remember someone using on old S_D was that to defeat Diana, you have to lock her in a room she can't get out of, or at least that it takes her long enough that you can do whatever it is you needed to do without her in the way. So, theoretically, beaming her down to the Terrasphere would be a good idea. She can survive the temperature and hold her breath long enough to swim/climb/burrow her way to the surface, but it would take a while.