The sound off her spell going awry and across the street half shocked Tonks, but the brief cry of the civilian woman that it hit was even worse. Tonks couldn't really worry about a downed civilian, sadly. Fortunately, she'd just used a light stunning spell and not something more dangerous. She knew the woman would be alright, but that might change if she continued to let her death eater cousin roam free, so she had to take a different tactic.
It was a quick bit of thinking, but the wild spells Bellatrix was sending out, and the smooth deflection of Tonks' first attempt fueled an spell she'd been working on for a while now but never had the chance to showcase. It was, essentially, a shield. But it was made to encase instead of protect. She focused her eyes, wand flicking hard in Bellatrix' direction as she growled across the crowd, "Penitenio!" And suddenly a field of energy appeared -around- Bellatrix instead of hitting her at all. Inside the dome like shield, spells could bounce but not escape. Outside, things were as normal. Tonks had no clue how long she had to keep the charm up, but it seemed solid for now, even if it took a good bit of energy to maintain.
"Now, Bellatrix, you can come nicely or I will put you down where you stand." Tonks stated coldly, keeping her wand lofted in the woman's direction so the shield charm held solid. Tonks even took a few more steps in Bellatrix' direction, feeling suddenly confident that her spell was holding.