The MIL's behavior is completely unacceptable. The DIL was merely sharing a cooking tip, and the MIL turned it into a ridiculous contest of who knows the son better. The MIL's insecurity and need to be right overshadowed a simple conversation, causing unnecessary drama and hurt feelings for the DIL, who was just trying to connect with the family.
This whole spaghetti saga reeks of attention-seeking behavior from the DIL. Why else would she corner her husband with such a trivial question in front of his mother? It's a blatant power play, designed to make the MIL look foolish and assert dominance in the family. The DIL needs to grow up and stop stirring the pot with such petty squabbles.
The MIL instigated the conflict by challenging the DIL's cooking habits and the son's preferences. While the DIL could have handled the situation with more tact, the MIL's possessive behavior and need to be right created an unnecessarily hostile environment. The MIL's subsequent text to the son further proves her inability to handle conflict maturely.