The answer to this question hinges on how one defines feminism. The aims and goals of feminism have changed over time; however, by the standards of the late nineteenth century, Kate Chopin could be considered a feminist.
Chopin's stories are about how women are constrained by society's expectations. Women were expected to base their lives around the needs of a husband and children. It was assumed that any woman who did not marry was a sad individual indeed, an "old maid" who was to be pitied. Women who sought work or fulfillment outside of a homemaking role were seen as eccentrics at best and dangerously subversive at worst.
The Awakening portrays Chopin's most radical image of a feminist woman in her heroine Edna. Miserable in her marriage and unfulfilled as a mother, Edna is a woman who wants to be an artist. While Edna is presented as being selfish, Chopin still sympathizes with how she was essentially forced into her position by a rigid set of social rules.
We also see this in "The Story of an Hour," a darkly humorous piece about a woman who feels freer when told her husband has died, only to die herself of a heart attack when her plans are dashed after her husband comes home safe and sound. "Desiree's Baby" shows both the sexism and racism of the Victorian era, how a woman could be destroyed her the men in her life. She is totally dependent upon men, and had better hope to have men far kinder than the cold-hearted Armand as a mate.
These writings were challenging for their time. They openly question the way things are, the things people took for granted as true when it came to women, men, and marriage.
So, Chopin is pretty feminist. Her stories criticize how women are locked into roles that might not be for them (the character of Adele in The Awakening is an exception, someone who is fulfilled by motherhood, so Chopin is not critical of women who want this role or motherhood in general) and how women should be prized as individuals, not as subservient add-ons to their husbands.