I mostly play Sedna and I don't lose many 1v1s early on in the game, except to rook if he sets up his farm before I can get to the lane. Either way I'm not actually going to die from the rook, I'll just get pushed back to friendly towers. Especially at level 2 with both pounce and heal you can chase people past the corner tower on cataract, get a kill and live if you're careful.
When I'm not playing Sed I'm mining it up as Regulus, and with both AF and Mines I don't have any problem targeting enemy monks early. The trick to killing Sedna is to run her out of mana and then call any bluffs, killing minions is a key part of this. High Priests heal 30% of Sedna's max health if they are buffed, which is in the order of 500 - 1000 HP, no DG can afford NOT to target the priests if tackling Sedna solo. In 2v2 you can gank without it, but that's another case.
Past killing the priests, slow stacking and stuns are the way to victory against Sedna.