Word for a task that is necessary, tiresome, and accustomed to?

I'm looking for a word that describes a task or act that you recognise and are accustomed to, but a "familiar task" had a positive colouring which doesn't quite capture what I'm aiming for.

In context, I want the word for a morning ritual which a girl has gone through her entire life, but takes no pleasure in doing so. Specifically, a cold and piercing morning shower to refresh herself.

"For a while, she confides in the familiar, mellow warmth of her bedsheets, but she knows she must get up. Her first choice is the shower, a ___________ that she knows she must do."

Solution 1:

It is not clear whether the OP wants a word to describe a feeling or a task.

The morning ritual -- the cold shower -- which the young girl must perform is a chore. The feeling she has about it is resignation, Merriam Webster

the feeling of a person who is prepared to accept something unpleasant

Example to fit the OP's question:

She approached the chore of her early morning cold shower with resignation.

chore as defined by Cambridge English Dictionary:

a job or piece of work that needs to be done regularly:

By the time he’d finished all the household chores it was mid-afternoon.

A chore is also something that is difficult and unpleasant:

It was a real chore trying to give our dog a bath.