How To Wean Of Off Latuda?

my daughter has been on an 80 mg dose of Latuda for over a year and now has had the dosage cut to 40 mg and will gradually go off the med. I have read the the best way to ramp down to avoid withdrawal is to cut dosage by 10 % at a time every two to three weeks or so. The Latuda only comes in 20 mg amounts. How can she reduce the dosage by 10% ? The pharmacist told her she can t divide the pills. Thankyou