Why the late MP5?
I never really run into mana troubles, her norther winds is a flat 45 mana, that pretty much recovers itself while its active. Soulshroud however does give it more consistancy. It put behind FM because this is a build that works of successful ganks, kills, and passive opponents. Feel free to change the order, as stated in the guide. But this is how i build, and enjoy her.

I don't understand everyone's hate on frozen mallet?
Its a good 700 health for a tank, and grants a further 40% slow?
Is it the slow effect because sejuani already has a natural slow? If so whats the problem with overkill.
Also CV, is really there as I'm usually the only guy that takes it, but i still found it good for protecting my jungle and counter jungling. I personally find that if your smart in your jungle though flash is not needed, neither ghost. i put them there as options for a reason, it depends on your own comfort level.

CV...? Not the junglers job... You need ghost or flash to escape counter-jungle ganks. Why the late MP5 item also?

Frozen mallet is not needed, and a jungler should never have CV. Thats the supports job.