*The AD runes and the low amount of MR is sole because the armor helps early and so does the AD for sustain. The basic attacks wont deal to much and the armor helps with that. Also the AD helps with CS. It makes it faster and easier to move from target to target. With some champs like Anivia the AD helps if that person didn't get armor. It helps do more damage then before.
*The LT and Rylits is simple. Landing a E into W and Q will easily do a nice amount of DOT with the passive from LT, then auto attack and pop ability as they come off of CD for more of the DOT form LT.
*The easy way to get around things is just positioning. The reason you need more armor on her is the ADC will focas if shes good. Ahri is a high priority because she has True Damage and has a very mobile ult. If Ahri can get the ADC out and dodge the AP moves then she is golden. My opinion is when facing someone like Ryze or Cass get an ABS for MR since they have Auto aim abilitys and can focus you very fast.
* Ahri can focus easily so allway see if you can land an E on their carry. A fast combo with E W Q will melt any ADC because of LT and Dcap.