I have had this champion for awhile now, been playing her alot recently to find her perfect role, I do like her in the jungle, but Support Sejuani is where its at.

The Rune choices speak for themselves, you will be building as tanky as possible, because you will be iniating most fights.. health,armor,magic resist all factor into a good tank

Again going with the rune choices, you want to be as tanky as possible, the little bit into utility helps for the mana regen, flash cooldown and extra speed to get to your targets faster

Start off with regrowth to sustain, then the philo for better sustain and the gp5, then start working on getting tanky, starting mogs, then FoN, and Spirit visage, I also reccommend if the other teams AD carry is getting out of hand to switch out spirit visage for thornmail.

You start with the q, because thats your bread and butter, that is your engaging tool. the permafrost needs to be maxed early because it does the most damage and the greatest slow she has. the w is good for late game when you have the good amount of hp, the damage scales well then.

Flash- get away
Exhaust- Stop them from getting away

Pros:

She's easy as balls to play
Very good engager
Ulti stuns EVERYONE for 1 sec, and stuns the person hit for 2
Good tank, with sustainability

Cons:

Not as strong damage wise as other tanks
Early game she's basically just a walking exhaust
People don't like her cause they don't know how to play her

Sejuani is a great champion, I will agree she could use a buff, but she is not bad by anymeans, she is a great jungle, even better support, she is on the level of nautilus as a support IMO. She has great engages and slows, if your AD carry is worth a damn you should run bot lane with my guide. Now go off and show them Sigourney Weaver don't play that ****.