TVLinerevealed the news, and now we're smacking ourselves for not seeing it before. MarySteenburgen certainly looks like she could be Pablo Schreiber's mother, and now that we think about it, it seems obvious that Pornstache's mom has more potential to cause trouble than any other mother character could.
After all, Pornstache is still fully convinced Daya is carrying his child. He's in jail, which means he can't do much about it directly, but there's nothing stopping his mother from swooping in and trying to make a connection with Daya.
Given that Daya's own mother is also in jail, we wouldn't be surprised if Mary Steenburgen's character shows up demanding that she be given custody of her "grandchild" once he or she is born — something Daya wouldn't want. Or maybe it's the opposite; perhaps she wants proof that the kid is actually her son's. A paternity test could land Bennett in major trouble.
Whatever the case, it seems clear that Daya's trouble are far from over.