Here's an idea: stop eating her good before a date.

Don't tell her you have a date. Don't eat with her before a date. Don't trust her to behave like a decent human being. It's not rocket science. And if this is the 4th time, then maybe YDi. Though no-one deserves a mother like that.

YDI for not learning by now

That's really shitty , just hope you don't date a back door man ...

Move out & stop telling her anything

She admitted to doing this? Wow! Stop eating before your date! Are you one of those girls that eats before a date,so that when on said date they eat just a Salad?

Don't eat the food, and then do the same to her.

OP, prepare your own food! If you're old enough to be going on dates, you're old enough to make your own food! That way, mummy wont be able to put laxatives in it.

When she ets the food on the table when she is not looking give her yours and u take hers

Don't eat the food, cook ur own. N two don't tell her you gotta date if ya gotta. That or switich ur food with hers