Up until Patch 4.70, Teela was probably the slowest Champion in Teleria. As a result she was really not a great champion.
With her recent buff, Teela is now at least serviceable although still not someone you should instantly invest in. Her best ability is to bring an AoE Leech but its on quite a long cooldown to be reliable. She does have a single target HP burn which is ideal for bosses but generally not for wave or spider 20-25. Ultimately you’re going to find better alternatives that perform the roles Teela brings better.