Warmog's has been slightly nerfed, which is just enough to put Frozen Mallet ahead of it for an Atma's build, so that's perfectly fine. However I find Frozen Mallet on Sejuani to be overkill, as she already has a heavy perma slow for all practical purposes. Instead I prefer Triforce for some much needed additional damage and other great stats(especially the extra movement speed and attack speed). I also question the need for Wriggle's, Sejuani isn't too reliant on her auto attacks, W does most of the work. The free wards are nice, but getting Philosopher's Stone and Heart of Gold faster is superior Imho. Sunfire is a solid option for armor+hp+more AoE damage, especially if you go with Triforce instead of Fromogs.

Why thank you good sir. I seems like I forgot to mention this item as well as atma's impaler. I had them up before but took them down as I thought they were not the best choices.

No warmog's option? Son I am disapoint.