Why didn't Gandalf or Galadriel warn Aragorn about Boromir ?

[Erendis]

Originally Posted by The Mouth of Sauron

Armed with that knowledge, why didn't Gandalf immediately send Gwaihir down river to warn Aragorn ? Come to think of it, why didn't Galadriel warn Aragorn even before the Company set off ? She certainly had plenty elven-muscle at her disposal to imprison Boromir.

Wouldn't both of these moovements be quite bold?In a Fellowship where all balances between its members were on the verge of breaking,capturing one of them under the blame of being possesed by the Ring would be the final heat.

And even if Gandalf sent Gwahir to Araagorn,first of all,they would wonder why Gandalf did not come with him.Secondly,since it was not certain yet whether Boromir would give into temptation ,the warning must have been personnal and discreet.And what would be more suitable than a giant eaggle?