Pumping breast milk on Shabbat

Greetings to the Honorable Rabbi,
A mother of a one-month-old baby, who is not at home on maternity leave but is a student and studies during the week. Every day she pumps breast milk with an electric pump so that the baby will have it for tomorrow. She produces a large amount of milk and if she does not pump for a long time, her milk will become engorged and the amount of milk for the next time will be reduced.
What is the ruling on pumping on Shabbat? Apparently, the milk must be spoiled in order for it to be a work of the Illach and a rabbinical prohibition, but is it permissible to save the milk that is milked on Shabbat for Sunday? I would point out that in principle the baby can breastfeed, and therefore this is not a matter of pikuach nefesh regarding Shabbat itself, but rather regarding the shortage that will occur on Sunday or the fact that due to not pumping, the normal amount of milk will be reduced.
thanks