All crime is evil -- but surely crimes against those who are helpless and vulnerable are among the worst. Only someone with no conscience could commit something like your mother experienced. The Bible labels as evil all those "who follow the corrupt desire of the sinful nature and despise authority. . . . They are experts in greed -- an accursed brood!" (2 Peter 2:10,14).
You've done the right thing by reporting this to the police. Even if they aren't successful in recovering what these scam artists stole, your report will help them be on the lookout for similar crimes in your area. They also can notify agencies in your community that have contact with elderly people. They in turn can alert the media, encouraging people to be on guard against scam artists. Remember the old saying: If it sounds too good to be true, it probably is.
In addition, if your mother is no longer able to take care of her finances, you will need to step in and help her. (An attorney specializing in elder law can assist you.) She may be reluctant at first -- but this situation indicates you may need to be more active in her affairs. The Bible says, "Defend the cause of the weak" (Psalm 82:3).
Urge your mother to be more cautious in the future. Don't condemn her, however, for what happened or keep bringing it up. Instead, pray for her and let her know you love her. Most of all, remind her of God's love for her, and of the hope we have of eternal life because of Christ.