She was a German Expressionist painter and printmaker known for her powerful and emotionally charged works. While she didn't paint a picture with specifically three owls, she did create a series of woodcuts called "The Three Owls" (Die drei Raben) in 1917. These woodcuts are often referred to as a single work, but they actually depict different scenes related to the theme of death and grief.
It's possible you're thinking of this work, or perhaps another piece by Kollwitz with an owl motif.