This is the smart plan:
@Marimo_420 you can try to block Tris tonight and if a faction kill still happens it means that you should have lied.
If @Tris admits to have been blocked and you admit to have blocked her and a faction kill doesn't happen, then it could mean that perhaps she simply abstained and she didn't faction kill. Or it could still mean that you blocked her instead of faction killing but at least no one dies tonight.
If @Tris claims you didn't block her then you are incapable to block and the liar.
@Marimo_420 you can try to block Tris tonight and if a faction kill still happens it means that you should have lied.
If @Tris admits to have been blocked and you admit to have blocked her and a faction kill doesn't happen, then it could mean that perhaps she simply abstained and she didn't faction kill. Or it could still mean that you blocked her instead of faction killing but at least no one dies tonight.
If @Tris claims you didn't block her then you are incapable to block and the liar.