Post apocalyptic society would probably bring about no periods due to starvation in many women.
The jacket could have been her fathers when he was a teenager or child.
And most important of all in a long term survival situation is to ensure you can keep some form of normality and comfort. A morning routine is great for this.
This is because your body weight can get too low to sustain a pregnancy. So to protect the body, the reproductive system “shuts down” because it's severely malnourished.
Women from postapo movies don't usually look or act no-period starved. Morning routine is nice, but you certainly wouldn't keep up with everything pre-apo even if you had the resources and time. You can make up apologies for almost anything in movies. That doesn't make these things look less ridiculous in general.