An easy way to beat bosses on PC without cheats is to change the ARK settings. (This can be done on singleplayer.) You can change the setting so that your creatures get huge amounts of hp/melee when leveled up. I am going to battle this with a 425 Rex that has 100k health and almost 5k melee
First tame a megladon an make scuba gear then go to gen and do the mission hide and sink on alpha 5 times it will give you 50 to 80 armor saddles you will now need 5 Rex's should be 70k life and 1500 melee go kill her on alpha with confidence that you shouldn't even loose a rex have fun making that tec rep
Megatheruim are just as good as rexes in this fight so bring an army of one or the other but the sloth bois will give you a TON of chitin after the battle which is great for making ascendant chitin gear and saddles.