Things have changed back & forth for women mids over the years. In my day (LONG time ago, I know), women had to have hair above "bottom edge of the collar" throughout their 4 yrs. Then it went to short during PS and whatever length (put up, of course) the rest of the time -- to mimic the USN/USMC standard.
Then, I seem to recall, women could have their hair long during PS. IMO, that was a bad idea b/c, other than Sunday mornings, there is simply no time to do anything to it -- even twist it into a bun -- and gives you another thing to worry about (hair falling out of bun). I was as feminine as they came and I NEVER even ran a blow dryer through my hair during PS other than Sundays -- just no time.
Now, it seems, they're back to something along the lines of what happened in my day. I suggest getting your hair cut at your usual hairdresser before you go. Err on the short side -- as noted, hair grows back. Yes, there will be a few tough months w/lots of clips as you re-transition from short to long after PS but women have been enduring that since day 1.
Finally, I can confirm what the men (I think) above have said -- your hair is the least of your concerns during PS. The guys have no hair! You're hot and humid (e.g., sweaty) all of the time. You're busy all of the time. Hard to explain until you've done it.
One other thing -- skip the makeup for PS other than for church on Sundays (if you choose to attend). It will melt and turn your Whiteworks into a complete mess. Fine for Ac Year but stay away during PS even if your complexion isn't the greatest. As noted, no one cares.
If women have any questions, feel free to PM me.