Some might say it was the caliber, but the .243 and good 100 grain bullets was plenty good enough! Other than you saying that she left a good blood trail, I'd say she was gut shot!
If not, it may have been a muscle hit somewhere. I once made the mistake of pushing a deer too fast, and trailed it for well over a mile. The blood trail finally gave out, so I don't know where it was hit either!