Haven't had the time to try her online, so this is colored by inept AI, but:
Yeti are incredibly survivable--I knocked down towers at 2 or 3 minutes in by yeti charge without taking any significant damage myself. Health regen aura makes pushing lanes really easy. With a little mana regen gear, a 1500 heal every 10 seconds is basically 150hp/sec, on top of the 30 from the health regen aura. 180dps is a decent amount to be mitigating. Throw in the fact that Sedna ends up with a decent amount of health and her extra 50hp/sec under 30% health and you can get away from enemy demigods (barring maybe Regulus) until you have the yetis to take them down.