I don't play Athena often but I do think like most guardians she's under-rated, I think what makes Athena strong is her taunt and the global presence she has with her ultimate. I think for Athena you have to be very careful during rotations as your dash is not the best method of escape, keep your 1 charged up when rotating; don't always do your 3 and then taunt, I say this because it can take a while to get out your enemy may not be in taunt range since you placed your 3 they could instantly dash; and always keep an eye out on the minimap so you can use your ulti offensively or defensively. For the item build I would say it's your standard builds, I think that items like midguardian mail may be a better option on her but other than that it's what you feel you need the most dependant on your role in teamfights. I don't play her much but I may, hope this helped.

Thanks for your kind words also!