Connie Willis is considered to be a writer of science fiction rather than romance. She has won multiple Hugo and Nebula awards for her novels and short stories, all of which are classified as science fiction. Two of her Hugo-award-winning novels -- To Say Nothing of the Dog and Blackout/All Clear (a single novel published in two volumes) should also be classified as romantic suspense novels, in my opinion.
Willis began writing at a time when there was a great deal of separation between the science fiction and romance genres. The recent growth of the paranormal romance and urban fantasy genres has really bridged that gap. Romantic suspense, both historical and contemporary, has also become a popular genre. Although I doubt that Connie Willis would wish to be classified as a romance author, she has often included romance subplots in her works, particularly the light, comic stories that are clearly inspired by the screwball comedies of Hollywood's golden age.
There were no romantic elements in her first two works about time-travelling Oxford historians from the late 21st century. The short story Fire Watch first used the premise to tell a story about the extraordinary efforts of ordinary people to save St. Paul's Cathedral during the Blitz. Willis developed her time travel universe more fully in the poignant novel Doomsday Book, about a grad student who observes the horrors of the Black Death in a much more up-close-and-personal way than she had anticipated. That book is beautifully written, and it always makes me cry.
I don't want to include any spoilers, because I want to recommend that everyone read these books. I read Black Out/All Clear a second time while it was all still fresh in my memory, because I wanted to see if Willis had continuity errors with her complex chronology. I was impressed for different reasons on the second reading, knowing everything the characters knew at each point in the story. I also realized that the heroine was attracted to the hero much earlier than I first assumed, which put an entirely different spin on the primary romance.