If she does not get the DUP to join her they are still allowed to form a minority government.
But if labour got everyone else to back them then they would probably be first choice and the Tory party would have to withdraw.
The Tory party will struggle even with the DUP. Dont think they would last that long without them.
Normally if the DUP withdrew after the opening of parliament the Government would be allowed to proceed as minority government.
Well that's the way I see it. But they would find it extremely hard to carry on unless maybe they hooked up with the Lib Dems.