I took care of one mother who had a similar situation a number of years ago.
Quite a sad case, actually.  This particular mom had a triple whammy.  At 3
months' pregnant, she suffered a stroke that left her paralyzed down her right
side for several weeks.  She fought back from that, got lots of
occupational/physical therapy (and me as a "private instructor" in infant
care, to help her learn to handle her baby despite residual weakness), then
developed pre-eclampsia & delivered 5 weeks early by c-section.  Pumped &
eventually bf without much problem.

Five weeks after delivery (on her DUE DATE, no less!), with baby home &
healthy & thriving on her milk, she too developed SOB, was rushed to hospital,
where she arrested in the ER.  Her OB (also mine) did open cardiac massage on
her, & said her heart had "turned to mush".  Apparently she had some sort of
autoimmune reaction, & her body "turned against" her heart, rejecting it as if
it were a transplanted organ.

Yes, THIS woman died...I ended up babysitting for the funeral (who else could
they find to leave a 5-week-old premie).  The "nice" ending to this story, was
that just before the family left for the funeral, I said, bitterly, to my
patient's sister, "How can she be in heaven if it means being away from her
baby?"  And the sister answered, "You just watch after we leave and the house
is quiet...she's still right there with him!"  Sure enough, after everyone
left, the baby woke and started to cry, but before I could get across the room
to him, he'd calmed and was smiling and gurgling, looking directly at a spot
by the side of his crib.....all I could do was say "Hi, Joanne".

So to make a long story longer, perhaps Kathy's mom had a similar autoimmune
reaction, just not as severe.

Carol in St. Louis, having just gotten home from teaching bf and having a
prolactin surge....