I don't think that the check fraud conviction (assuming there will be one here) can be used as an aggravating factor because she was not a convicted felon when she committed the murder, but rather, she would have become a convicted felon after she committed the murder but prior to her murder trial. I did a little looking around and found this:
There are fifteen aggravating circumstances set forth in Florida Statute § 921.141(5), the first is pertinent here:
¹(a) The capital felony was committed by a person previously convicted of a felony and under sentence of imprisonment or placed on community control or on felony probation. (found this at:
http://www.leg.state.fl.us/Statutes/index.cfm)
When Casey committed the murder, she was not a previously convicted felon, nor was she under sentence of imprisonment or placed on community control or on felony probation.
I am not a lawyer (yet!) but the way I read this is that since she wasn't already a convicted felon when she committed the murder, it cannot be used as an aggravating circumstance to convict her of 1st deg murder.