Severus dodged the brunt of the stinging hex, but it grazed his shoulder and he hissed out a breath. He was impressed that she could cast at all, the spell was meant to be debilitating. It only lasted for a few seconds though, and when she got up she was going to be angry. He needed to act fast.
A wordless spell put up his own shield and his wand lashed out, flinging a good old fashioned disarming spell. He didn't know if it would penetrate her sheild, so he followed it with the lockjaw hex, just in case. She'd be limited to non-verbal magic if it worked.