I love what’s already been said, but I’d add one thing: I would think about how bad the conversation would be if you have to fire her, and aim for a somewhere roughly half as bad as that when you talk to her. IOW, you don’t want to wish later that you’d been more firm if you have to fire her, but you have to balance that with the risk of demotivating her by making her feel that she isn’t valued.
I love what’s already been said, but I’d add one thing: I would think about how bad the conversation would be if you have to fire her, and aim for a somewhere roughly half as bad as that when you talk to her. IOW, you don’t want to wish later that you’d been more firm if you have to fire her, but you have to balance that with the risk of demotivating her by making her feel that she isn’t valued.