I presume here we are talking about an individual who had no female sex organs before surgery. I presume a male had his male genitalia removed and was given a plastic or artificially created vagina of a kind.
I think that any Catholic pastor would have to refuse to witness a ceremony uniting a male to a female transsexual. If such a ceremony took place, I believe, a Catholic tribunal asked to judge the case would declare the marriage null and void.
Said my tribunal source, "One who is biologically and physiologically male at birth may have his genital organ altered to resemble those of a female, but he remains essentially a male. He is thus incapable of marrying another male."