My "good" tenant has snuck a dog in? What would you do?

[mrfuji70]

Here's the scenario....

I have a two bedroom townhouse that I rent out in the suburbs of a metro area. I have a single, 23 year old tenant who has been living there problem free for the past year. She is very well paid in her job so she takes very good care of the place, and pays the rent on time every month and in some cases before. A couple of months ago, asked if she could have a pet because she was thinking about adopting a Yorkie. I told her that's fine as long as she pays a $250 pet deposit and the dog is under 10lbs I would include such a clause in the new lease (she informed me she would be renewing) . As a perk for renewal, I gave her one month's free rent ($850).

My tenant has a twitter account which is not set to private so I can simply google her name and her posts come up (call me a snoop, this is business). Upon doing so last week I discovered that she has had a dog in the place since last month--she posted all of her dog's activities in my place on her twitter page. We scheduled the lease renewal for this weekend and upon meeting with her, she informed me that she decided she wasn't going to get a dog because she works too much and wouldn't have time to take care of it (even though her twitter account says otherwise). I was more miffed that she lied than that she had the dog inside without my consent or without paying the deposit. I informed her that if she did change her mind, to let me know as I would not care to have her sneak in a dog. She said she wouldn't do that ever.

So now I'm at a crossroads. She's violated the lease terms, but she is really a good tenant overall and I have not had issue with her before. Part of me wants to act a fool about the situation, while the other half says look the other way mainly because it is extremely difficult and costly to find tenants--let alone good ones--in the area as of late. The economy has taken it's toll on the private rental market here. So I ask, what would YOU do?