Are you guys delusional asking for Lohan? You do realise she's 30? Ariel is supposed to be 16.....
Of course they won't actually cast a sixteen year old, but they definitely are unlikely to hire anyone above 25ish.
Look at Beauty & the Beast - Emma was 24-25 when she was cast + filmed for the part.
Not to mention Disney wouldn't let Lindsay ANYWHERE near another film, come on
Personally I think it'll be a relatively unknown actress, certainly not a Hollywood A-lister, just like they did with Jungle Book + Alice in wonderland.
