“McSally likely had her current constituents in mind when she agreed to sponsor the first measure. Arizona’s 2nd Congressional District, which extends southeast from Tucson and shares a border with Mexico, tends to swing between Democrats and Republicans. Gabby Giffords once represented the area, and her aide Ron Barber took over not long after she was shot in the head during a constituent service event in Tucson. McSally unseated Barber in a 2014 race so close it ended in a recount. Hillary Clinton won the district by nearly five percentage points even as McSally won re-election there by nearly 14 points. Co-sponsoring an immigration bill like HR 1468 seemed to make political sense then.”
I guess this is the explanation.
McSully is too committed to Ryan/McConnell leadership. It is hard to say she supported a DACA bill just to appeal to her own district without acknowledging she must be un-genuine.