Ashe is generally an adc without escape so the thing you have to do is to try to play decent and not overextend try to poke with your w skill and make one autoattack because now her w applies a "stack" and you can make a critical hit when you hit the target so you don't have to auto attack your enemies 2 times and that takes time and you might get even get poked for that and lose the trade.

Now the reason i use crit chance runes and no atk dmg is because i want to maximize her passive by doing that i get to go to 208% crit dmg when having infinite edge and phantom dancer just imagine the damage! And if you think crit runes are going to disturb you in farm you think wrong ashe always crit in her second autoattack so you can easily farm that way.