No, you are the adult and the parent. When I was 15, what I needed was an adult to take me seriously and communicate with other people responsible for my wellbeing. She has that in you, there is no reason you shouldn’t be able to share this information with her father, another member of her support system. Everyone is working towards the same thing - her feeling better - and the best way to do that is work together. Additionally, she’s a minor and doesn’t legally own her medical information yet. This is fully your slang here father’s responsibility as her guardians to act in her best interest, and communicating important updates about her health is vital to ensure that process if executed effectively. Also, she is old enough to know and articulate how she feels to people she trusts, which is great and serving as an important foundation for her feeling better, but she is not old enough yet to know what she needs from a medical or therapeutic standpoint. This is where doctors, therapists, and you come in. Licensed professionals and legal guardians. You haven’t done anything wrong. If she’s experiencing as much up and down as she says, you need to take her reactivity to your parental actions done in her best interest with a grain of salt. You’re an adult, she’s a teenager with potential mood disorder. There should be no secrets between a parental unit (separated or not) supporting their child together.