A good Ahri should eat her for breakfast.
Ahri´s Q goes thru minions and does good damage. taly has a strong skillshot but is blocked by minions and unreliable in comparison.
Ahri is VERY mobile. Tali not (you can count ult, but ahri´s ult is way more offensive oriented in a 1v1 than talys´s. So that goes to ahri.)
Ahri has a nasty CC in her E, which has long range and is not unforviging at miss. Tali has a risky , unreliable closerange CC that pops her enemies away, or brings them too close, and can be used only with her E for damage...and not so great damage.
Ahri has a damaging ult. Taliyah doesnt.
Ahri can clear waves faster. Tali not only struggles and minion clear...but she is a mana drainer. Both are, but Ahri´s use of mana is WAY more rewarding than taly´s....waveclearing speaking.
All taliyah got against Ahri is better ganks on bot adyacent lanes and jungle.... but on a 1v1...a good ahri should capitalize. No 2 ways about it.