You should tell someone it could really hurt them. You may think keeping it to yourself is a favor but the best thing to do is to tell someone. I know it's hard but in the long run that's what would be best
You should tell. If the problem is dangerous which is better losing your friend and knowing you could have prevented it or knowing you prevented something bad from happening and have your friend be safe and ok?
Sounds like you need to be discussing the whole situation in more detail (than is possible on this app) with someone u trust. However, if there is a real risk your friend may suffer serious harm, if you dont tell, then you should. Is there anyone who you respect and trust who you can maybe talk to abut this, someone who you can trust to keep it confidential, (unless they feel your friends safety is at risk)? Someone who can help you work out what to do next, who wont blab without good reason?
I understand how you feel I've actually been in this situation myself and I think I know the perfect solution. If she told you something dangerous then you should tell, you might think because she told you not to tell and you might think that it'll cause her more pain your wrong, you're actually helping her. You might think you're being a bad friend, but you're not cause you're looking out for her. You should be scared bout what she told you and if you feel like you can't stop her yourself then tell somebody how you fell and maybe that person could help you. It might work and if not maybe that was what was suppose to happen. I hope everything is ok! Good luck! ☺️ just make sure you tell because you will do her a huge favor and I promise... She'll thank you later😉