Because she actually took the time to read the Amendment? (Unlike some of the idiots who voted for it who were too blinded by hate to even bother reading it first, aparently.)
The first sentence defines marriage, which the second sentence then proceeds to ban.
(A) Marriage in this state shall consist only of the union of one man and one woman.
(B) This state or a political subdivision of this state may not create or recognize any legal status identical or similar to marriage.
Under the plain wording of the Amendment, anything identical to marriage (of course, the only thing identical to marriage is marriage itself) may not be recognized in Texas.
Haven't these folks ever taken a basic logic class?
Everything is identical to itself.