I have recently moved out of a rental (09/01/2012), and as of October 30th, I still had not received my deposit back, nor a letter stating why my deposit was being withheld. I sent a certified letter to the landlord stating that the 30 day time had passed and that she owed me the deposit in full, or I would sue her. I received a check from her in the mail, but she took out money for carpet cleaning. The carpets were not cleaned when I moved in, and she did not ask me to clean them when I moved out (month to month verbal agreement). I did, however, clean them with a rental carpet cleaning machine. I live in Colorado, and am under the impression that the carpet cleaning would be a normal wear and tear item that the owner was responsible for. Should I sue her? I believe in my state I can sue her for up to three times the amount of the deposit. Please help!

In some states if the landlord does not send you a written accounting within the required time then they are not entitled to retain any of the deposit for any reason. So we need to know which state this property is in.

How much did she withhold

Under 38-12-103 of Colorado Revised Statutes:
(2) The failure of a landlord to provide a written statement within the required time specified in subsection (1) of this section shall work a forfeiture of all his rights to withhold any portion of the security deposit under this section.

However, there are some rules about how to go about it (Renting: Security Deposits)

She could be held liable for treble damages if you give notice within a week.