Praise be to Allaah.
It is better not to name one's daughter Malaak, for two reasons:
1.The meaning of Malaak is malak (angel). There is an element of exaggeration in giving this name to a person.
2.It is a name which is well known among the Christians, and it is (Arab) Christians who pronounce the word malak as Malaak. There are many good names in which there is no element of doubt concerning them, and those names should be used in stead of names which are problematic or doubtful.