I mean if you're worried about some arbitrary power level, then sure, app some story everyone's heard a bajillion times. There's nothing wrong with it. Though you do already have a legendary magical girl, so im not sure why you're scared of making a fable.

You can also just get creative with how your magical girl's fable affects her powers. Is stripes arguably the weakest magical girl in an RP about huge groups of girls teaming up and beating on bad guys? Yea. Does she have really niche situations where she can punch way above her weight class? Absolutely. Anyway, it's just the start of the RP and Stripes managed to save someone already, so I don't think fables are automatically powerless trash tier plebs.