Before he started the war, Frederick made Maria Theresia an offer: He'd buy at least parts of Silesia and accept her on the throne of Austria, or even support her (not sure). She declined.
If instead of Fredrick his not that bright brother Frederick Wilhelm had been in power... he either wouldn't have asked for Silesia, or if he had, she might've said "well, your house has some old rights for Silesia... let the court decide" and until a decision at the court has made, years have passed and she's won against everyone else who dares to attack her.
Could work... Frederick is killed by his father because of his homosexuality (the Soldier king had a bad temper...), and his brother becomes king.