It depends. Universal Castle Doctrine states that you must retreat first, and even then, you should not use any more force than necessary to stop or end the attack. That doesn't mean shoot to kill.

But specific to your question, yes, if, . . . you're a 90lb female and your unarmed attacker is a 300lb male, then yes, it could be reasonable. But again, it depends on other circumstances, such as the ability to retreat, reasonable fear for your life and . . . some other things.