I think she would have had the potential to become one, like how Amy was born into it but still wasn't as powerful as Willow.
But I don't think if she hadn't have started messing around with Magick it would have happened, her magick seemed to grow after a big even, like Restoring Angels soul started it, then after the joining spell in season 4 she became allot better then she went all dark on glory in Season 5 and brought Buffy back which lead to season 6, then the slayer activation spell seemed to lead to a Willow able to do anything she wanted in Season 8 comics.