If Sejuani gets nerfed it should only be changes to her base stats and early clears
I could see something like -3 base armor to open up chances to counter jungle her and prolong the time it takes her to get to lanes early and/or hit level 6. Maybe shave a little off her base HP to.
I think Sejuani is a lot healthier than say a champion like Zac was, and even though she is frustrating to deal with I'd rather she not end up overnerfed like zac, especially when her ban rate has never even come close to his.