Men have their skills and benefits and Morrigan has hers since she's a woman. Although she can transformer herself into a man, she prefers sticking to what she knows best and she uses her assets quite effectively here.
But thanks to Flashback moving his hand down to Morrigan's butt in order to feel it, it gets in the way of Cassius's intended move to get the shape-shifter's attention. It's bad timing, but Morrigan expects something to go wrong. So when it does, she's ready.
Flashback feels the tap on his hand and he's surprised as he breaks the kiss and looks down to notice something he was never meant to see. In a flash, he scrapes a dagger across Morrigan's cheek and in the middle of shape-shifting into her true form she says, "Bad move."
As expected, Flashback tries to run but Morrigan used her Meta-Tech power to give her watch a 'tractor beam' capability. So as the speedster tries running off he is surprised when he doesn't get very far as he slows down to a crawl before being lifted off his feet and forcefully pulled back towards Morrigan.
With a smirk, Morrigan slams a fist into his face as she tries to knock him out. But Flashback proves how resilient he is by taking the punch like a champ. Unable to run away, he is forced to fight. And while Blue Ghost is faster than any ordinary human, Flashback is far faster than her. He hits her hundreds of times in the span of just one second and she crumbles to the ground as she is unable to withstand such a punishing move.
Fortunately or unfortunately, Morrigan still has that watch that is functioning as a tractor beam. Gotta love Meta-Tech that gives technology a super power. This means Flashback cannot run away and that means Cassius can do something.