The month devoted to "Women's History" is almost over, but I decided to assemble a shortlist-- aided by various Trina Robbins works-- as to some of the early (up to 1980) landmark comics-creations of female creators, whether alone or in collaboration with male creators: This is not an all-inclusive list: just a snapshot of the more notable accomplishments.
1909-- Rose O'Neill creates a somewhat intermittent series of cartoons and/or comic strips called THE KEWPIES, which become a marketing sensation in the early 20th century.
1934-- Martha Orr creates a soap-opera strip, APPLE MARY, that is revamped into the better known MARY WORTH by other hands later on.
1935-- "Marge" creates LITTLE LULU as a one-panel strip, though the character becomes more famous through cartoons and comic book incarnations.
1940-- Dale Messick creates the comic strip BRENDA STARR
1941-- Tarpe Mills creates a female superheroine in MISS FURY.
1965-- Ramona Fradon collaborates on DC's METAMORPHO
1972-- Marie Severin and Linda Fite collaborate briefly on the short-lived THE CLAWS OF THE CAT from Marvel Comics.
also in 1972, Trina Robbins edited and contributed to the underground WIMMEN'S COMICS
1978-- Wendy Pini's co-creation ELFQUEST debuts.
also 1978-- Rumiko Takahashi debuts her break-out comic URUSEI YATSURA
There are various other works by female creators, but these seem to be the standouts prior to 1980, though I admit to knowing little about the European scene.
Any additions?