they found out that she's allergic to peaches, so they'd discretely put peach shavings around her making her cough, and the poor dad made the rich mom think that she had tuberculosis...and the final touch was him squeezing a packet of hot sauce onto a pile of tissues the maid tossed into the garbage can, making the rich mom think that she was coughing up blood
so the rich family fired the maid because they were afraid that she might end up infecting them