Women are harder to caricature than men for a variety of reasons. Many people usually struggle in order to make these caricatures look feminine and more often than not, caricaturists feel that women end up looking like drag queens.
It is not true that women are harder to caricature as the caricaturist only needs to keep in mind the difference between masculine and feminine features.
The facial elements to differentiate are thick eyelashes, fuller and redder lips, a soft complexion, thinner and more curved eyebrows as well as high cheekbones. These are features that women accentuate or create for themselves.
The differences in the faces are under the skin in the form of the skulls and bones. The differences are that in males, due to testosterone, the bones are enlarged, and due to high levels of progesterone they are taller and have narrower pelvic bones. The jaw bone also helps in the differentiation of males and females.
Female skulls are smaller, and the mandible, as well as brow ridge, is less pronounced. It is also wider than the male's skull, and that is why the features are softer. The jawline is less prominent, but cheekbones are more prominent. The areas which are above the eye sockets are more blunt in men, and the brow is more pronounced. Women have a sharper area in it that is why their brow does not protrude that much.
The jaw of a man is more wide and more square. The female has a shorter and rounded chin as compared with a man's wide and high chin. The noses of females are less angular, and they have a softer and smaller tip. The nose is also narrow, shorter vertically as well as pointier.
To make the caricature look more feminine, you should not play around with the brow ridge, chin or jaw or if you want, make it smaller. The features which should be enhanced should be exaggerated instead.