03 Honda brake problems

My girlfriend has a 2003 Civic and at 30,000 miles the rotors were warped. Honda wanted $400 to turn the rotors so I did it myself, cost $18. The brakes felt like they should after having the rotors turned and we have been extra careful on the brakes ever since, using the transmission to slow down, etc. Now at 45,000 the rotors feel warped again, wheel shakes above 60 MPH when braking and surges when you come to a stop. Is there something that can warp the rotors other than the braking habits of the driver?
 
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