Couple of different responses depending on whether this is in person or via text and how threatening she wants to be!

1. Send a link to Lily Singh's how to make a sandwich video. Tutorial and a burn all in one
2. Have a blank face and then slowly let it become a sickly sweet smile and either simply say "okay" all cheerfully or if they're slow drive it home with "you can totally trust me with your food!!" all with a sweet sweet smile and a nice tone of voice- scares 'em every time
3. Let your face show how stupid you find what they just said and then just hold that expression. Keeping holding it. Hold it until they start falling over themselves to retract their statement. You can hasten it by saying words like: wow, ick, yikes, pass, ew (my fave)
4. Build me a house, cut down a tree, [pass away] in a war, aka tell them to do a "manly task" first!
5. Leave 'em on read. They may or may not catch on and self correct but either way ur depriving them of attention, which is what that statement wants.