Your sentence is absolutely natural. A native speaker would read it without stopping. The rhythm, the logic, the phrasing — all clear. Here is why it works: “Blew a tiny dispute out of proportion” is a classic, idiomatic use. “So that she had to step in and calm them down” also sounds normal and fluent. If you want alternatives, here are the most natural ways to use both expressions. ✅ How to use “blow out of proportion” Meaning: exaggerate something, make it seem bigger or more serious than it is. Natural variations: They blew a small issue out of proportion. He tends to blow everything out of proportion. The media blew the incident out of proportion. Don’t blow this out of proportion; it’s not a big deal. ✅ How to use “step in” Meaning: intervene, get involved to stop, guide, or control a situation. Examples: She had to step in before the argument escalated. The manager stepped in to resolve the conflict. A teacher stepped in when the discussion got too heated. Someone needs to step in and set boundaries. A couple of smooth rewrites (just stylistic options) They blew a tiny dispute out of proportion, and she had to step in to calm them down. They took a tiny disagreement and blew it out of proportion, so she stepped in to settle things. They blew a minor issue out of proportion, forcing her to step in and defuse the situation. Your original sentence is already strong. These are just stylistic flavors.

This is almost perfect! I'll just change one thing. "They blew a tiny dispute so out of proportion that she had to step in and calm them down." Grammar point: so X that Y Meaning: She waited, then stepped in and calmed them down when the dispute grew into a big enough fight. You can also say: "They blew a tiny dispute out of proportion, so she had to step in and calm them down." Grammar point: X, so Y Meaning: She stepped in and calmed them down because the dispute grew into a fight.