If this is the first time you've approached the subject of her abusive partner, go easy on her. Mention that you've noticed her partner doesn't always treat her with the respect she deserves, and that this has made you worry. Listen to her response. Be prepared to hear denials and excuses. Asking your sister questions is more effective than telling her what to do, says Casey Gwinn, president of the National Family Justice Center Alliance. Ask her how he makes her feel and if she thinks he has changed since they were first together.

Tell your sister you're there for her. Ask her what you can do to help. Begin by telling her how wonderful you think she is, rather than concentrating on what a bully her partner is and how she's foolish to stay with him. Make her feel that you're on her side, not fighting with her, says the BBC. Bear in mind that she may still be in love with her partner and not yet able to imagine a future without him.

If your sister is ready to leave her partner, you can help her in many practical ways. Find out if there is a Family Justice Center in your area, where she can get counseling and legal advice. Call the National Domestic Violence Hotline and tell an advisor that your sister is being abused. Encourage your sister to write down all instances of abuse and keep all threatening texts, emails and letters. This may be required as evidence if she has to apply for an order of protection. If she has any bruises, scars or other bodily injuries, go with her to see a doctor for medical proof of the abuse. Help her pack her belongings and create a checklist of things she needs to do, such as changing her cell phone number and her bank account. She may need you to take her to see a lawyer. Ask her if she wants to stay with you until she finds a place of her own.

Your sister may leave her partner and then go back to him, possibly more than once. Diane Lass, Ph.D,, who works with victims of domestic violence, says it can take seven to nine attempts before a woman finally breaks free of an abusive partner. Let your sister make the transition in her own time, advises clinical psychologist Patrick J. McGrath of "Ask Dr. Pat."