So kind of like the body saying it needs a rest?
Yes. Pregnancy and childbirth is hard on the body whether it's someone's first baby or their 20th and comes with risks and possible health problems (eg anemia).
She seems to get pregnant again pretty quickly after having a baby, so I would wonder if she is letting her body recover enough inbetween pregnancies and birth. Especially with C-Sections, but it also goes for vaginal births, women are advised to wait at least a 1-1.5 years (it varies from country to country but that seemed to be the lower estimates) before trying to conceive in order to allow the body time to recover fully from blood loss and the lost nutrients which result from pregnancy and childbirth. Getting pregnant earlier than one year shouldn't be a risk but continually getting pregnant without allowing a period of recovery might be, if you see what I mean. Multiple C-Sections can lead to scarring, depending on how the person heals and how the C-Section went, which can make future deliveries difficult.
Her age might be a factor too. Women over 35 are slightly more at risk of problems during pregnancy, such as premature birth; problems with the birth; or problems with the child, such as gentic abnormalities such as Down's Syndrome and Edward's Syndrome. Problems can happen regardless of age and many women over 35 have easy pregnacies, births and healthy children, but studies have shown that there is a slightly higher risk with older mothers with certain problems.