Hi, and thanks for your query on eHealth forum!
Post injection site pain and inflammation is treated with ice packs and pain killers. If your doctor has advised against it, then please ask the reason for it. Usually it is advisable to use a buttock on alternate days so that it gives about 24 hours time for the area to heal and for the medicine to penetrate into tissues and reduce further inflammation. For now, please give her an oral pain killer and discuss this with her doctor as it is important to take the medication.
This reply to your query is just for education and counseling purposes and cannot be an alternative to actual visit and treatment by a doctor who can examine you. Hope this helped you in making an informed decision about your health. Take care!