Thank you for waiting. You're right to be concerned about your friend's advice to dig a tunnel and bury the turtle. If your friend has had success with that method, she has been very lucky. A turtle should never be forced to hibernate. Turtles naturally seek out the level in the soil where the temperature is safest - we don't know how to do that. Hibernation is a dangerous time for turtles of every kind, and even in the wild, many don't survive the winter. When we humans interfere, it becomes even more risky. If a turtle eats too much during the last few weeks before hibernating, the food will not be digested, but will rot in the stomach. That leads to fatal infections. If the turtle hasn't eaten enough during the summer to store enough fat to last through the winter, it will starve during hibernation.
Normally, box turtles will hibernate when temperatures are consistently in the 40's, but if the soil hasn't yet cooled off, many will wait until it does. In nature, when temperatures are in the 40's and 50's, many box turtles don't hibernate at all, but simply slow down for awhile. For Lila's sake, the only thing you should do is provide good places if she chooses to hibernate. Your ideas of tilling the soil, placing lava rocks, and adding some of the hay sold for rabbits are all good. You can take her to the place you prepare so she knows it is there, but don't try to force her into in any way. It's better to rely on the turtle's instincts than to enforce what we think is best for them. Some people hibernate their turtles inside in the refrigerator, but this procedure requires careful preparation. The following sites have more information on hibernation:http://www.boxturtlesite.info/dvmhib.htmlhttp://aboxturtle.com/hibernation.html
In summary, it is best if the only thing you do is prepare a good site, then leave it up to Lila. It's possible that she isn't mature enough for hibernation to be triggered (they often don't for the first few years) , or that she doesn't feel cold enough yet. Leave it up to her.
If you have more questions, let me know in a REPLY. I wish Lila a successful winter, however she chooses to spend it.
My goal is to provide you with excellent service – if you feel you have gotten anything less, please reply back, I am happy to address follow-up questions. Please remember to rate my service only after you have all the information you need. Thank you!