Alan,
How much injury did she sustain from being hit by a car? How long after being hit by car did she lay those eggs? The egg you found could be an old- pre hibernation egg that you just found. Or it could be that the temps you have the turtles in are not at a true hibernation temps and therefore it may still be possible for her to produce and lay an egg. What is the temp? A trully hibernating turtle should not be feed.
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Tess Cook
www.boxturtlesite.info