[Fiction question] What would a well-dressed woman have worn to the ballet in San Francisco in 1910?

It’s not just a matter of finding out what dressy fashions were like for the year. I want to know what a woman would have worn to attend a performance such as an opera or ballet, and specifically if she’d have worn something on her head; if so, what kind of hat or headdress? I would think that people would have avoided wearing something that would obstruct the view of those behind them, but I don’t know if that courtesy is just a matter of present-day custom or not.

I want my character, a well-to-do woman, to wear a hat or some kind of headdress, but only if someone of her class and station would have done that.

What’s a good resource for information about period fashions, including the types of occasions for which the styles would have been worn?