Welcome. My mom has been diagnosed since I was a child and she told me what she was diagnosed with when I was 8 and she had to go in-patient. The diagnosis didn't bother me, but her having to be admitted was hard on me. I think 14 is old enough to have an open conversation about it, but perhaps you could discuss with a therapist who specializes with children for an idea on how to approach the subject etc.

As far as what the teacher told your daughter I would suggest voicing your concern. It doesn't mean you need to disclose your diagnosis, but such an ignorant statement should be corrected. I hope you find this site supportive.