Regarding my wife’s fast on Yom Kippur. My wife is (bsha’ah tova) in week #12. She still nurses our 16 month old daughter 3-8 times a day, who can drink liquid from a cup but doesn’t drink formula. Our daughter has a birth-related issue with her esophagus which affects eating, so the doctor encouraged continued nursing in addition to her solids.
My wife is concerned about the heat (we have no AC) and dehydration primarily connected to nursing, in addition to her age (44 years young).
Ideally, she wants to fast normally, but doesn’t want to endanger her health. With that in mind she wants information regarding the permissibility of drinking/eating shiurim if necessary.
She should drink a lot before the fast and spend the day in bed if necessary. Even if it means not being able to daven, fasting is the primary mitzvah. The baby should be minimally nursed and not at all if possible [i.e. the milk won’t dry up and the baby can deal with replacement food/drink for a day]. This should be enough to get her through the fast. If however at some point she feels very dehydrated or very faint, she may take shiurim to regain her strength and hydration.