Our lease ended July 30, 2011 and we told here that we weren't sure if we were going to stay here or not. She said that's fine and we can go by month to month till we decide. Now that it's December she did another year lease but dated to back to July 1, 2011. Well I signed it and started putting today's date on it 12/7/2011 and she told me to date for 7/1/2011 so I crossed it. She said it will be complete and finally when my husband signs it. I told him not to though because of the back date. Is it illegal to back date it and can I still do something even though I signed it?

In fact back dating is to your advantage. Basically the landlord is saying this new lease will take affect when the previous one ends, so, unless you want to commit for another full year the advantage is yours. The only reason I would sign it is if it included a retroactive rent increase.

There is nothing illegal about except for that. She can't go back and collect more.

... The only reason I would sign it is if it included a retroactive rent increase.
...

If it includes such an increase, I would hesitate in siging it.

Otherwise, it is in effect a 6 month lease.

Yes, nothing wrong, it shows a continued lease. And allows you out in 6 months. But then it also allows the landlord to raise the rent in 6 months when it is time to renew a new lease.

Whoops I meant to say wouldn't sign it if it included a retroactive increase.

No increase in rent. It's identical to the old lease it's just dated 7/1/2011 till 7/30/2012 and just now making the new lease in December for me to sign to cover her back from July.

I don't see a problem in that. Its definitely not illegal.