This image is from Walker’s 1814 book. You can see that some of the women are in Empire-waisted gowns (like the beauty who is front and center), but others are still in 18thC garments. The rural beauty is in a round gown, with an apron, mitts, handkerchief, and a cap and bonnet. The woman on the left with her back to us is of particular interest, as she’s wearing her stays (possibly leather ones from the look of them) as her main upper garment, along with a handkerchief, an apron, and a short petticoat. The woman on the far left appears to be in a man’s coat, and the one just behind our rural beauty is in what I think is a form of smock (smocks could be either shirts or coats that were work over your other clothing to keep them clean).
The only information I can find about “lowkers” is that it’s a form of “looker” and is related to looking after something. So perhaps these women are so labeled because they are looking after the field/crop.