Well, there's three possibilities:
a) This is just theatrics aimed at extracting some side concessions (probably over NI backstop)
b) May did not get the kind of guarantee she thought she did from Merkel
c) Merkel has betrayed May (either voluntarily or her hand has been forced by others)
It's probably 'a'. I'm fairly confident that 95-99% of Chequers will pass, there will be some kind of fudge on the remaining 1-5%, and a load of journalists will let us know by tweeting 'Breakthrough!' at 3am on a Sunday morning. This will be followed by gushing 'insider accounts' of how Michel Barnier single-handedly saved the Brexit process or some shit.