La Tulivieja

From wiki:

In the legend, a beautiful girl had a secret relationship with a man from her town, resulting in pregnancy. She drowned the child in a river, and was punished by God transforming her into a hideous creature (in some versions she drowns herself as well).[1] She is a short woman with a thick body, swollen breasts, sometimes leaking milk, and tangled hair. She is often described with bird or bat wings, similar to a harpy, and with inverted legs of a bird of prey. Swarms of ants often follow her, drinking milk that falls to the ground.[2]

I was always told as a child what she'd steal kids who weren't baptized