Is it permissible for the mother or father, especially the mother, to see the prospective fiancée on behalf of the son (the suitor) to inform him of her characteristics before he sees her himself?

There is no harm in the mother or sister looking at the fiancée to describe her to the suitor. However, it is not permissible for the father to see her if she is not one of his mahrams, due to the generality of Allah’s Almighty saying: (Tell the believing men to reduce [some] of their vision and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do), and His Almighty saying: (And let them not expose their adornment except to their husbands or their fathers or their husbands' fathers...).