I feel like Kindred is surprisingly balanced for a new release. Rewarded for skill, check; adequate counterplay, check; damage dealt is proportionate to performance, check. She is missing a clearly defined niche, as well as clear strengths and weaknesses, but I'm sure those can be ironed out eventually.
I think it's a good thing that she can go to a minimum of 3 roles (mid, jg, adc), and I really hope Riot doesn't nerf that away in an attempt to force her to be the "jungling marksman" they envisioned. That said, I think it's prudent to re-allocate her ridiculous sustain and possibly rethink her mana costs. I understand that she needs high sustain and a spammable kit in order to jungle, but when that free sustain and spammable kit are taken into a lane, it becomes a bit annoying. Not overpowered in the slightest, but slightly annoying.
The best solution would probably be to a) make her sustain exclusive to hitting jungle creeps, b) increase her Q mana cost by a bit, and c) decrease her W mana cost by a bit in compensation. It would address her insane lane sustain, as well as make Q-trading a bit more difficult in lane without hurting her jungle clear.
As it stands, she's decent but not great, and definitely not on-release broken (read: Kalista) or on-release underwhelming (read: Lucian).