Um..if she was so "Revenge Obsessed", she probably would killed Bjayzl long before she did here. She saw an opportunity present itself and she took it. Whether you thioink her action was justified is a personal matter, but I wouldn't call her 'obsessed'.
Just curious: Did you have a similar action to Picard taking out Ensign Lynch with a Machine Gun on the 1701-D holodeck back in 1996 when "Star Trek: First Contact" was in theaters <--- and do you despise the film or the character of Picard as a result?
IMO - I had NO ISSUE with 7 of 9 showing that she was in actuality a Human being who believed that, for kidnapping and stripping former Borg of their Implants (to make a profit) - and who did so to someone 7 of 9 considered akin to a 'son'; Bjayzl should be executed, and did the honors.
I like her character traits better than the constant hypocrisy of Picard, which is displayed nearly every episode of this series so far. Funny thing is: It's EXACTLY the same way his character was written fior the majority of TNG. If their's one aspect Picard LOVES to showcase, it's his blatant hypocrisy.
Or Kirk's "Let them die" comment?