Could the landlord come after me?

[jojo]

I moved out of a house that my ex and I had rented, both our names are on the lease.  I moved out on 10-25, on 10-27 I left a message on the landlords cell phone and mailed her a letter saying I had moved out.  She just called my work today, said she didn't get the letter or message and the rent has not been paid for December, my ex is ignoring her calls.  Can she still come after me for the rent?
It was a month to month rental agreement and it has been past the 30 days that I gave my notice.