Coffee, there is no unwittingly about it. May has stitched them up.
There is now someone else she can blame for the whole fiasco. So far, British negotiators and politicians have been blaming the EU, Ireland, Varadkar and anyone else they can think of. They can now also blame Foster and the DUP. And if the DUP walk out (which they should, surely they can't stay supporting this conservative government?) she can blame them for the fall of the government, the new general election, and the complete falling apart of the (I think non-existent) progress so far.
The more people they can blame, the less responsibility they have to take themselves.
We all knew this wasn't a runner; don't tell me May didn't. She isn't that thick.