Near-'totals' don't always mean disaster. Speaking from experience, our 2000 SSEi was literally a thousand dollars from being totalled becasue of the catestrophic damage rendered to the transaxle (the left front wheel was the point of impact.) Intitial estimate at the time was ~$13,000 on a car then worth $14,000. When it was all wrapped up, the total cost - including follow-up repairs and problems that cropped up later - came to what I'd approximate as $16,000.
The car had about 55,000 miles on the clock and ended up with a zero-mile transmission, supercharger assembly, axles, suspension componants, electronic hardware, and rebuilt engine in addition to sheetmetal, glass, and interior repairs (amazingly, no frame damage whatsoever). All this guaranteed for life.
So, what to hope for depends on your intentions - if you're going to keep it 'till it dies, then you can come out of a major repair with alot of new parts with extended warranties unto themselves. If you're worried about resale, fuggedaboutit; its unsellable. Any dealer who even gives you a good deal on trade-in will junk it and that's something we couldn't bear considering our car still feels and looks brand-new.
I will assume if the car skidded laterally that there will definitely be alignment and drivetrain damage since the IS is rear-wheel drive. Of course, frame damage changes the entire scenario and in that case, the best may be to indeed have it totaled. I'm pretty sure it won't be quite the same after a frame-straightening. I know Ocn will find this and be of tremendously more help than likely most of the rest of us could be. I know he helped me get an idea of what to expect when my Olds was hit...twice...in the same two months.
Anyhow, I assume your sister is okay...if so, I'm glad to hear that. Oft-repeated here, but cars are replacable; people aren't.
Good luck and let us know what becomes.