I had to leave my apt during the second year of my lease. I called my landlady on the 8th of the month and told her I was leaving. She said that wouldn't be a problem as long as I kept paying the rent until it was rented again. I agreed to do this. On the 20th of the same month she called and told me that it was rented as of the 1st of the month. She also said that she had decided to keep half of the security. There is no damage to the property and she is not out any rent money. Can she do this?

ANY question on law needs to include your general locale as laws vary by area.

Your landlord is required to give you an itemized accounting of how your security deposit is used. If the uses are not justified then you can sue her.

But frankly you are getting off lightly. You broke your lease without legal notice. To get away with essentially a month and half is lucky.

Nope.
Do a search for Tenant's Rights in your state. You have very specific rights which will be spelled out in detail. You will most likely need to file an action at the local level, usually a magistrate's court. The cost for this is small and you generally don't need an attorney. Just be prepared, have copies of rent receipts/cancelled checks, etc. Before and after pictures are great (although it may be too late in this case, it is still good to know), also keep a written log of all that has transpired, including conversations with the landlord and what was said. Good Luck!

The landlord agreed to void the lease - providing another tenant was found - which is what happened. He also stated that she lost no rent money. Most states allow for this, so the landlord is essentially taking half of the deposit just for fun.

Comment on ScottGem's post
The landlord agreed to void the lease - providing another tenant was found - which is what happened. He also stated that she lost no rent money. Most states allow for this, so the landlord is essentially taking half of the deposit just for fun.

Did the landlord agree? All we have is the OP's word on that. Does he have any proof that the landlord agreed? Did the landlord say there would be no penalty for breaking the lease?

Please read my response. I specifically said that the landlord has to give an itemized accounting and if the items are not justified he can sue.

My other comments were expressing my opinion about someone who breaks a lease like the OP did. Generally breaking a lease involves a 2-3 month penalty. So my opinion is that the OP is getting off lightly.

However, there are ways the landlord may be able legally use deposit. For example, the landlord might be able to charge for the costs of advertising and vetting a new tenant. The point is we cannot say with certainty that the landlord cannot legally keep a portion of the deposit. Its true she can't just decide arbitrarily to keep it. But we don't know if that's the case. We also don't know where the OP is or what laws cover this situation.

And many leases have clauses where the deposit is lost in case of default.

So without reviewing the lease it will not be known either.