Took me time to figure her out. Suffered a big losing streak over it, but I found some helpful advice and managed to improve my game with her.
This is her core.

Then you go straight tank with maybe one additional AD item.
For runes, I run Armor Pen reds and Quints for early damage against champions, Flat Armor Yellows, and Scaling MR Blues.
Masteries, I go 0/12/18
In Cunning...
Wanderer for reaching allies in time to help and returning to lane relatively quickly after shopping or dying.
Assassin, no contest.
Merciless is another obvious one.
Dangerous Game, again...duh.
In Resolve
Unyielding is just slightly better than Recovery for a Tank with no self heals.
Tough Skin to give you an edge in early engages against opponents.
Runic Armor to make the most of your passive.
Insight is just too OP not to take.
Swiftness for the Tenacity and Slow Resist.
And, finally, Grasp of the Undying for additional sustain and damage.
Summoner Spells I prefer are Ignite and Flash.