[@Melkor]
You can't be a skilled bender and also keep loosing control. While General Zhao burned everything, he didn't lose control in the same way. Every one of his fire attacks were deliberate, he was just volatile, brash, and such and he didn't think about what happened when he missed and hit other things. He was only focused on his anger and goal. Aang lost control from the lack of respect and skill in firebending because fire is more 'alive' and can do it's own thing more then other elements without the control. Something like lighting an oven shouldn't ever be that devastating for someone with skill. Loosing control of that amount of fire is only for novices. So while your character understand it, I don't think she is 'skilled' in it's use even if she was defending someone. Of course if you mean something else with your wording then I have read please feel free to explain!

tl;dr - if she is afraid to use it and looses control, she wouldn't be a skilled fire bender even in the action of defending someone. Learning the control is the first step in the practice and fearing it wouldn't lead to her being a skillful fire bender at any point.