Can I charge a tenant for vacancy after they leave?

[Brian Barfoot]

I have a tenant who has been notoriously bad with communication. Her lease is due at the end of the month and we wouldn't mind either way if she stays or goes. I called her a few days ago and then texted today to find out if she wanted to renew and she hasn't given a clear answer. My concern is that if she doesn't renew we won't have time to properly advertise and will have a vacancy for a couple of weeks. Can I prorate the time and take it out of her security deposit for not giving reasonable notice? The contract says she has to let us know within 45 days of termination of contract (which was 20 days ago.)