Could be Vitamin K.

I'm definitely guessing it is something commonplace, but not overly abundant. The two girls we know still had plenty of pills left, while the hacker one ran out even though she has been taking pills as payment from the other escapees. This of course assumes all of the escapees divided them equally when they fled.

The two girls have been eating lots of wild herbs and plants, some of which are probably rich in Vitamin K.

The real reason I think it is something readily available is the fourth girl shown in the OP. She obviously shows up after this, so unless she's a future defector, she's surviving somehow.