It's a dangerous move, but once you've made your decision, you're committed. Now all that matters is how you go about it.
You wait just long enough for Corliss to shift her focus back to Ward—then you let her have it. You slam your fist into her back with bone-crunching force, sending her stumbling into Ward's reach as she exclaims with surprise and anger. Ward doesn't miss a beat, ducking low and smashing into Corliss's chest with his shoulder, driving her back and keeping her off-balance, allowing you to follow up with a second strike of your own.
Corliss's ribs crack as your fist slams into her chest and you follow up quickly by driving your knee into her solar plexus. She doubles over with pain, barely managing to twist to the side and avoid a vicious kick from Ward. She pops back up again quicker than you expected, a dagger suddenly in her hand which you barely have time to register before it plunges into your chest. She's faster and stronger than you anticipated, but you should know better—she has the same gifts as you after all, and she's had over a century to hone them to perfection. Then again, there's only one of her and two of you. You're able to ignore the pain and counter the attack quickly enough, ripping the dagger from her grip as Ward lands another blow before stepping back out of range of any retaliation.
"Keep her there!" Ward yells, pulling a familiar-looking handgun from a discreet holster at his belt. "Keep her from running!"