The purpose here is to have many Ap and be able to survive.
She is playing in support most of time, pushing tower and can survive in 1v1 or escape.
She is more played with this build, for staying behind others heros and launching is ulti in middle of teamfight. She can be play, tp into ennemy group, ulti, hourglass. But it's not my favourite, because if your teammate run away or aren't coordinate, you will die lot of time and ennemies will go away with low pv but alive.

Need magic penetration. It's better than Ap for her. And with soil you can deal extra damage.
Reduce cooldown of course, because long cooldown for her's spell.

Because in the beginning we don't have AP, need to up soil lvl 3 faster. Indeed this build is expensive, so you will need to farm a lot, and with soil lvl 3, it will be easy and usefull for pushing. Care, most of time you will be near ennemy tower, so take extra care for miss.

Ignite for finish ennemy without risk life under tower(good too againt regen heros, like Mundo).
Flash for escape or be closest ennemy for launching Dark binding. Usefull too for your ulti(in premade only!), if you feel like a goddess(with good teammate, you should survive and make lot of kill/assist);)

With these items you will get a lot of ap and could survive most of time.
In first extra mana for staying farm creep on your line. Don't try to much to kill hero.
And most ennemy will under-estimate you.