All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
In principle an agent is not permitted to act according to his own will, rather he should act according to what he was entrusted to do. However, since it is most likely that these organizations call to Christianity, it is not permissible for him to give these clothes to them. The scholars set a condition that what one is entrusted to do should be permissible.
However, he should not do whatever he wants with these clothes, as this might be a reason of condemning the trust of Muslims. In our view, if this lady is a Christian, one has to give her back these clothes and apologize for not acting as an agent for her. If this woman is a Muslim, she has to be advised that these clothes should be given to a Muslim charity organization or to poor Muslims. If she agrees, all perfect praise be to Allaah, if not, then one should not act as an agent for her and should give her back her clothes.
Allaah knows best.