Criminal sentencing (especially in property crimes) goes up with each conviction. The degree of the increase usually depends on the severity of the crimes commited, the significance of the criminal history, the defendant's history of supervision, the strength of the case, the underlying motives for the defendant's conduct (greed, drugs, etc) and countless other factors.
One thing you will need to be prepared to explain to the prosecutor is why the delay from the time she commited the crime and the time you filed charges. Normally forgery cases are taken very seriously but you will have to convince the prosecutor that this fiance of yours did not have authority or permission to sign these checks in your name. The prosecutor will have a serious burden of proof to meet so you must be convincing in your report and testimony.
Contact your local prosecutor's office and make a appointment to speak with them. They are really the only ones who can answer these questions for you. Take all your paperwork down there and talk to one of them. They will be able to describe the process to you as well as listen to your concerns. They will also be able to look at her criminal history and give you an idea of what the local judges usually sentence someone with her record and current charges. You pay these people (prosecutors) so use them!
Good luck to you.
I am not your attorney. This forum is for general questions and answers and I cannot provide you with applicable law or legal opinions or advice in your jurisdiction. Please seek the advice of a competent attorney in your jurisdiction. While I can answer general questions and discuss general legal principles, I cannot give you legal advice in your state. The internet is a great place to get general information but should not be seen as a substitute for the attorney-client relationship or the services of a good lawyer in your state.