Might have been sold is a passive construction that may better be “she could have sold.”

A large sum may need to be stated in its full form: “a large sum of money” (Barclay).

And given to the poor is translated “and the money given to the poor” by Good News Translation (compare New Jerusalem Bible, New English Bible, New International Version, New American Bible) so that no one will think that the perfume could have been sold and yet at the same time be given to the poor. Phillips restructures in a slightly different manner (“Couldn’t this perfume have been sold for a lot of money which could be given to the poor?”), while Barclay has “… a large sum of money, and the proceeds could have been used to help the poor.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .