Ironically enough, Emmeline was probably one of the most willing to work with him. She didn't need to trust him in order to do so. Others might disagree with her, but as she had the most reason to distrust him (so far as she knew), she was likely to be able to persuade most others.
"I'll pass that on," she said. How much information they'd be willing to share probably depended on the person - how much they trusted Severus, and how useful he could potentially be to them. "I certainly hope you'll choose to fight with us, if it should all come down to a battle."
That was what bothered her about all of this, in truth. There were no duels to be fought, no battles to be won. There was no war, not anymore. She wanted a war, not this middle ground - a war in which the lines would be drawn and everyone would choose a side.