Veronica was the nanny who cared for Aaron while Kate was on trial. When Kate returned home, the two hugged, and the nanny told her that she had just put Aaron to bed. ("Eggtown")
Veronica continued to work for Kate as Aaron's nanny after Jack came to live with Kate. Veronica typically got off at 4, but one night, she worked late while Kate went out to do a favor for Sawyer. ("Something Nice Back Home")
Trivia
Tania Kahale also portrays the admitting nurse that ushers Claire into the hospital in the flash sideways timeline. It is possible they are intended to be the same character. ("What Kate Does")