Living in Toowoomba Queensland Australia, trying to identify this plant.
Gaura lindheimeri (or Oenothera lindheimeri). The taxonomy seems somewhat unclear; The Plant List gives Gaura lindheimeri as the accepted name and Oenothera lindheimeri as a synonym, whereas many other sources refer to Oenothera as the current name and Gaura as a synonym or "old/ previous" name.
It is a popular garden plant and there are many named cultivars sold and cultivated, however it looks like it is becoming naturalised in many parts of Australia with the potential to become an environmental weed.
The links below contain images and info: