IF the assistant told the pharmacist-employer upfront, and the employer was fine with it.
Pharmacist's assistants are there to assist the pharmacist, not the other way around.
Or, here's a thought: The assistant can work at a pharmacy that doesn't stock such drugs.
It's all about inconveniencing the woman who's picking up the prescription.

Should a butcher shop have to accommodate a cashier who refuses to scan a customer's pork purchases?