re:
"but when it comes to killing his wife she doesn't get a chance to fight back..."

True, but, reading "naked" to mean "unarmed" the Lord gives Matty the better of his two weapons;
Then;

You shall strike the very first blow,
and strike it like a man.
And I shall strike the very next blow,
and kill you if I can.

Matty gets one this chance to survive, if he can kill or disable Lord Arnold/Darnel/Whatever then he won't be killed.

At least the Lady gets two chances!
one: Matty wins
two: She's pragmatic enough to answer
Who do like the better of us ?
as a survivor rather than a lover.

Remember by the values of her society she's the villain of this story and yet she gets a better chance than the chap she seduces !
( Noble blood d'you see, can't be goin' round killin' nobility willy-nilly. Give the oiks some uncommon rare ideas. ;)

AndyG