Keeping the Winter Soldier down was a good plan, he was fast on his feet, fast with his hands, at least if he was off his feet, she could slow him down just a little at least. 
His bionic arm jerked back to life, but not quick enough for him to sufficiently fend off Stephanie. He went down, back heavily smacking off the floor sending up a cloud of dust around them. She was trying to pin him down of course, trying to keep him down. 
The Winter Soldier fought back of course, lashing out wildly like a cornered cat. His fighting switched between terrifyingly precise and calculated, and downright blind thrashing. 

Natasha was coughing  and struggling to regain the strength to pull herself up. The knock had really winded her. 

She rocked slightly on her feet, finally upright, sucking in a breath, she steadied herself, only to find Steph and the Soldier grappling on the ground. The Soldier struggled to try flip their positions, to pin Steph beneath him, but she was a slippery one. 

Natasha waited till the Winter Soldier could struggle free to try choke him from behind, tugging him back with tremendous difficulty. He clawed at her. 
[b]"Cap- Cap get him now"[/b] she managed to shout, her grip beginning to loosen.