why would you report them? You hired her (under the table) and then you cut her hours. And she quit. Oh well. you couldnt afford her, and apparently, she needed more money. Life goes on....seems kind of vindicitive to call the cops on someone just because they quit working for you. And does she break the apartment rules? maybe, but why is that your business? thats between her and the landlord. Unless the other pet is directly affecting you, such as peeing on your floormat every day, then that issue is between them and the manager. If its a good manager, they will catch on sooner or later anyway, if not, well, oh well complaining likely wont fix anything anyway.
My advice? just let her quit and move on with your life. No need to stick your nose in her business or get her in trouble with the IRS just because they want more hours then you can give them. Just hire someone else.