So here's the deal. I am a team lead of a small company and I have a junior who is an idiot. I mean literally, idiot. We code in Python mostly and as Python is not structured as a default Java or C# project, the developer needs to be very careful so that the structure (or tiers) is maintained properly.

Now this girl, always messes up the tiers. Say one enhancement can be easily implemented in the UI tier, she would do the implementation in the core Db access layer, which may complete this particular enhancement, but breaks all the other functions (sometimes the whole project) connected to that particular module of the Db layer. She doesn't do any integration testing after updating the code, she only checks the current enhancement she is working on. When the enhancement goes to the testing phase, the testers find those broken functions and that results a re-work (most of the times done by me).

I have warned her. Even our manager has warned her. She always tells that she is working to improve herself. But I know, she isn't. She mostly chats with her boyfriends (yes, with an 's') when she has no work to do. She never upgrades herself or works on her skills.

I can easily report about her, and they will fire her without any warning (they did it already with a guy earlier). I don't want to do that again. What should I do? Any suggestions?

Oh, she has a great ego. She thinks that knows and understands everything. She will listen to your suggestions carefully, but will never follow those.