Alright this will be a pretty crude build off the start because I just wanna get something out there. I'll start with a brief description of Sejuani in my opinion. I see her as a hard CC/ initiator tank. Literally all of her spells slow, then a spell that increases the slow and then an AOE stun. What more could you want in a team fight?

Attack speed reds for the faster jungle. Armor yellows for the safer jungle. Magic resist blues for the extra tankiness or cooldown reduction blues if you want. Then hp quints for extra early tankiness

Go wolves first if you can get them done fast enough. If you can do them and get over to blue by 2:00 at the latest then do it. If you manage to get wolves first then go blue, then wraiths, then wolves, then red, then gank or get wraiths then golems. If you just start at blue then go wolves, then wraiths, then golems then red.

If you want, you can go for lvl 2 or lvl 3 ganks. I think lvl 3 would work the best because then you can have your charge, AOE slow, and then permafrost. It'll be pretty hard to get away from that even if they have flash. When ganking and you know the person has flash, wait for them to flash and then immediately use permafrost and you'll be able to catch up with the gankee.