Tell your mother: "My girlfriend's horoscope is wrong, her birthday is right, but the time is wrong." In order to prevent her from counting again, you can find another time to calculate privately and choose the best result for her.
There are many fortune tellers on the computer now. Try a few more, choose the best result, start to calculate with the computer in front of my mother, and then tell her: "fortune tellers who set up stalls can lie, and computers are the most scientific and will never lie."