she's responsible for the choices which led her into a compromising situation ripe for manipulation.

he's not right for blackmailing her like that, so he's only responsible for abusing her trust and possibly an intention of financial abuse.

but murder is a lot worse of a crime than blackmailing a rich, possibly also manipulative and unfaithful murderer, because material damage can be fixed/compensated or even ignored while a killing cannot be undone.

it shouldn't be framed as a matter of gender relations imo:

she's a murderer
he was a manipulative cunt

he's dead, she will go to jail

fuck them both

case closed.