Star Wars: Rogue One Trailer 2 - 14 Major Plot Clues
5. The Rebellion Send Jyn Unassisted
It was fairly widely assumed that Captain Andor would be assigned to Rogue One as the sort of official overseer of the project to keep the criminals and rogues under control and on track for their mission. It made sense that he would be the man tasked by Mon Mothma of keeping an eye on and leading the squadron into battle.
Apparently not.
It's only when Andor actually seems to volunteer to go with her that she gets any sort of offiicial Rebellion leadership assistance. That suggests we can assume that Jyn is initially sent off alone on her suicide mission (with a remit to recruit others, since Andor presumably sells himself to her with the "I have been recruiting..." line).
That goes to show either how much math Mothma has in Jyn, or how little she has in the mission (no resources probably indicates no assumed success rate).