I make sure our visit is jam-packed with excitement so my mother-in-law has a weak heart
So you are trying to over excite her then? Why?
Because she deserves it.
Excitement can trigger heart attacks, cardiac arrest, strokes, and other potentially fatal medical emergencies. You should take great care not to over-excite your mother-in-law if her heart can't take it.
You don't know her, she's an evil person.
You still should not try to get her worked up. You should not knowingly get her worked up when you know how weak her heart is.