Dawn calmly explains to Joe that she was certain that the criminals wouldn't kill him and leave them with no way to get at the money; Dawn had planned all along to still share the money with Joe as they'd originally arranged, and so she had merely taken the money in order to keep it from anyone who'd pursued Joe.
Dawn explains to Joe that she was certain the criminals wouldn't harm him and leave them without a way to get at the money; she had already planned to split the money with him as they initially intended, so she took the money to prevent others from getting it.