A brother’s wife is referred to as a sister-in-law. This reference lets others know she is related by marriage through her husband. A person can have multiple sisters-in-law.
Say, "This is my sister-in-law, Amy," when introducing her to others in conversation. When speaking to a sister-in-law directly, simply use her first name or given name.
For more than one sister-in-law, specify which sister-in-law is being referred to by using her first name when introducing her to other people or referring to her in conversation to avoid confusion. When speaking of more than one sister-in-law, use the plural sisters-in-law to refer to them collectively. Alternately, refer to them as relatives or family members.