Sejuani will take a pretty massive hit to early game tankiness upon the arrival of patch 7.21. Her base armor is dropping to 22 and the scaling is being reduced by 25%. Additionally, her base MR is being cut by 5 and scaling down by 40%. If you are playing a carry/assassin jungler, consider invading her after your first or second camp. After this, it shouldn't be hard at all to keep her behind.