Isabelle was supposed to be a badass cold hearted assassin sniper, all i've seen is a weak leftitst who tries to save everyone's ass and spends her time whining about some guilt they should feel, 'cause they're soooo evil people.
Killing living targets is her everydays job and she should be tough, i think Braga would've done the job well if her character was not that lame.
Connor on the other hand cried at one point but she was a normal girl a waitress, who became a "soldier" and despite all her training and her strong will, she couldn't snuff Dyson because she deeply respects Humanity.After all she only destroyed a terminator 101 and no human.
So, Isabelle is nothing compared to Connor/