Call Animal Controll NOW! I'm all for the "Permanent Borrowing" idea. However since you said she had no tags, if you happen to see her in the park again there's nothing stopping you from taking her home with you. Then you can either keep her or contact your local rescue for help.
I'm a "hot head" when I see anybody or anything being abused physically or verbally, especially if they can not defend themselves. So if it happened in my neighborhood I probably would be in jail right now.
Please keep us posted.