Legal Question in Family Law in Illinois

How many people do you think have been killed by civilian "witnesses" who attempted "citizen's arrest." Also the principle of CA only applies to misdemeanor arrests done to yourself. So my answer is NO and my advice to you is that you either stay out of your friend's business or you contact the police on her behalf and be prepared to go to court to testify against her significant other over her objections. Also be prepared to lose a friend.

That people even feel that they can act like the police and detain someone in 2010, without serious risk of injury or a lawsuit (or being arrested) is amazing. Do not go down that road, and call the police. If they take no action, there is little you can do.