This could be two people, but would normally be written with a different separator: "Betty, a maid; and a cook" (just removing the comma doesn't help because th

This could be two people, but would normally be written with a different separator: "Betty, a maid; and a cook" (just removing the comma doesn't help because then Betty could be a maid and a cook). As-is, the implication is that this is three people. If you would like to make that more explicit, you would instead re-structure the sentence†, so it's not highly relevant to the serial-comma-vs-no issue. †For example: Betty, one maid, and one cook. Betty, and a maid and a cook (a little awkward) A maid, a cook, and Betty (depends on how you want Betty's inclusion to land for the reader)