Daan, the PROG designator is biological.
The current rule says that the oldest biological female/male is the PROG.
Why is it so impossible to think through an ancestry scenario for women that doesn't reference the men? We don't do it the other way around. A man's mother-in-law is as irrelevant as a woman's father-in-law to their status as biological PROG.
Just as the most senior/eldest male member of a bloodline is the PROG 1,
so is the most senior/ eldest female member of a bloodline the PROG 1.
If numbers of sisters came out together, we rank them the same as if numbers of brothers did: PROG1, 2, 3 according to age.
If an SV/PROG's mother is the eldest female to come to this country, then she is the PROG (her marital or mother in law status is exactly as irrelevant as it would be if she was an SM)