OP i have the exact same issue, Ashe is my second most played and trying to succeed with her is immensely difficult.
People have high range, dashes, speedups, blinks and who knows what else to just ignore the slow and do their thing, many of them also deal their damage far faster than Ashe does which makes it hard to even activate her Q before dying unless its already stacked on something.
It doesnt help that burst is insanely high right now, stomrazor, duskblade, buffed ignite and what else adds up so much damage that is basically meant to let a assassin playing well kill a marksman with selfpeel and a janna on them if the botlane pair cant stunlock that assassin right away.
So your damage takes too long to dish out, getting caught means instantly dying and your range isnt even all that much better than everyone else, and they have stuff like dorans shield and lifesteal if you should start to become annoying with it.
Then they all just outscale you so you cant go anywhere near them without dying.....stormrazor+zeal item.
This creates a situation where the only real option is to sit back very far, play passively and never do anything unless your jungler is around.
Which will tilt the ever living hell out of most of your supports, i´ve been there.
Of course its not entirely hopeless early but its still hard, Ashe is somehow meant to be a scaling champ with her passive and Q after all.
So my conclusion is unfortunately that Ashe is really not worth the effort, you could have twice the rewards for half the effort on someone else like kai sa, lucian, draven or even Jinx&twitch.