Too Much TV

I've struggled with TV lately and tried a ticket system which I've abandoned and plan to try again later. With 1 child napping and the older one, Stacy, waiting for her to wake up, I don't know what to do with her! So we switched from TV to computer games. I have discovered that computer games don't affect her as negatively as watching TV. She doesn't become as defiant or zoned out of reality. I felt horrible about allowing Stacy to play on the computer for 2 or more hours while her sister Emma sleeps. I also only allow her to play games that have an educational or social aspect. Once she's on it's difficult to get her off, so the new rule is she has to stop when her sister wakes up and Stacy can't start until after 20 minutes of quality time with me. She gets to pick between reading or Wii Sport.  So far she chooses reading every time! I keep following the same trick of requiring some task before she gets the reward. I do that with eating as well. After she eats all her food groups she gets the desert.