The leaves of the plant look like those of a lily - which is the first clue. It's a perennial, and tends to spread. Although the bloom in this photo of the plant in her yard is small, and therefore harder to verify, it might to be an Alstroemeria, more commonly known as Peruvian Lily.
In one of those serendipitous moments, her question helped me identify a plant in my daughter's new yard that I wasn't sure about. Turns out it's an Alstroemeria psittacina.
Judy, if your plant is indeed a Peruvian lily - and I'm not convinced it is, so I'd like to hear from others - be aware that it self-seeds freely if not deadheaded.