Druid's ghosts in Wintersun now give ~9k xp for each kill + there is a ton of xp in the first 12 islands of the dlc 3 (if party is strong enough to clean them). Now lvl 13 is a possibility even quite early in chapter 3, if you do Wintersun asap.If you can cast legendary proportion in Blackwater it means the party is at least level 13 so basically you are doing it at the end of chapter 3 ,and with the DLC 3 shop that sells endgame gear! So basically you are agreeing with me, she needs extreme measure to make it work.
And it is not about Aivu herself, she is, first and foremost, extra move action for strongest unit in the field - MC. Pet classes do not need it as much, but it is amazing for those who do not have a mount naturally, and starting from the MR 4 she is sturdier than Bismuth .