It was traditional to wear a hat, but in the 1960’s, Jackie O popularized wearing mantillas (veils), and so, she being the fashion icon for females in that era, many Catholic women and girls would emulate her choice in the department.
As the above poster noted, the headcovering was required from 1917 to 1983. Therefore, it is no longer obligatory. However, many females do continue to veil. I see several women and girls in my parish, in no small number, do it at mass. No one cares, no one rudely points them out for being “old-fashioned.”
If you want to do it, great, go for it. If you don’t want to, you don’t have to. You should note, however, that it is common practice in many Tridentine mass parishes to request, but not require, females to veil. This is not, obviously, all-encompassing for Tridentine parishes, though.
FYI: I’m a guy. How do I know this stuff? Reading CAF does it to you.