The DJ turned up just in time to appease the crowd. If she didn't come in time, it would have degenerated into a full-blown riot.
There is a slight difference between *turned up in a timely fashion" and "turned up just in time"; the latter suggests a higher sense of urgency and is preferred; from the context of this passage, especially the noun phrase full-blown riot, we see such an urgency.
For further brevity, we could replace the phrasal verb turned up with another verb, like arrived or appeared, etc.
We could also use the situation to replace the propoun it, which has no antecedent.
The DJ turned up/arrived just in time to appease the crowd. If she didn't come in time, the situation would have degenerated into a full-blown riot.