Is it very possible for her sister to get a 10+ year prison sentence?

Your statement describes what the law calls "Assault", When you are the victim of a crime you should call the police. There are also various causes of action at civil law where you can sue for money damages.

Impossible to answer your question without knowing the charges or the person's prior record if any. Also depends on if you are an adult or a child. If you are an adult, I would be surprised if the prosecutor pursued a ten year sentence for this type of conduct, and frankly, it may not even be eligible for any charges that come anywhere close to that.

The information you have provided, while certainly relevant, is not sufficient to answer the question you posed. You have clearly been through an ordeal, but the question of how long of a jail/prison sentence might be imposed on the actor will also hinge on other factors. First, has the actor even been charged by a prosecutor's office? Second, if so, what charge(s) were filed? Third, what is the actor's age and what is her criminal history?
If you have not already done so, you should contact law enforcement to file a complaint.