How have police obtained consent to search a woman's home for methamphetamine?

Police officers served an arrest warrant on defendant's boyfriend at her apartment. After arresting the boyfriend, the officers obtained defendant's oral and written consent to search her apartment and found a glass smoking pipe and a baggie of methamphetamine in a bedroom. Defendant was advised of and waived her right to remain silent, to the presence of an attorney and, if indigent, to appointed counsel (Miranda v. Arizona (1966) 384 U.S. 436 [86 S.Ct. 1602, 16 L.Ed.2d 694]) and admitted to the officers the methamphetamine was hers.