All Barbera wants to is killing people, collecting teeth, getting high and ironically, Gabriels killcount is much MUCH higher in this chapter than hers. She got some of the Hermanos crew at the first weapons shack raid.
And yes, the twins are gone. terminator killer machines killed off by a shelf.
At first, this was way more complicated with Gabriel thinking they were about to shoot Bob - which is still the case but not focussed on. And she sets of a chain reaction with the shelves. It was just too unlikely that the twins wouldnt see her walz in and attack them.