I am really stern about stuff like this because I've read sooo many articles in the news about how some novice landlord got scammed by a professional tenant because she didn't do a background check, didn't get rent upfront, didn't have a signed lease, etc.

Not saying that this isn't a good investment for some people but wanted to warn you of its title.

Smiling and understanding, but firm, gave warnings, then 30 day notices.  

I would give them a warning that "house rules" do not permit disturbing/harassing other tenants and that there have been some complaints.  

Originally posted by @Max Tanenbaum:Maybe wait to address this at lease renewal time.I would let her know that it's not allowed and warn her about damges, then I too would address this at renewal time.

It can lead to many fines and fees along with legal issues; buyer be warned!

I would suspect that the overwhelming majority of tenants, you will have some other warning sign that they are abusive towards pets. 

Well, not the agent, but somebody from the insurance company can come out and do an exterior inspection at any time, without any warning.

Everyone tells me to fight this with ComEd, however I have been warned this will be a struggle.Has anyone ever had this happen to them before or dealt with ComEd on anything like this?

Just a friendly warning:  rent is not guaranteed because of a lease.