Men wore trousers women wore slacks.
The war years had introduced many women to slacks.
I imagine this girl has chosen to wear these, aware that the picture will be in colour.
They probably fastened with buttons or a zip at the side. Zips were almost unavailable long after the war had ended. Here the tight fit around the hips could not be trusted to hooks and eyes or pop-fasteners.
A woman would not normally, for example, wear slacks to work in an office. They were confined to holiday and leisure wear.
About 19 years old date about 1949 Estimate born 1930 ± 3 years