Is my Friend Mentally ILL?

Your friend does sound as though she has changed a lot. However, the thing is if she does not or cannot acknowledge she has a problem, then no one will be able to help her. She has to be willing to reach out for help. You sound like you are being a good friend that cares for her very much, but there are somethings that you cannot do for your friends. I know because, my best friend has depression and health problems and we have been friends for 40 years. No matter how much I try to get her to go out to do stuff together she always refuses by making excuses why she can't. Therefore, the best thing to do is be there for her by giving support. In my opinion, it could be that she has been lured into a church that can do things like that to a person or the stress has triggered a disorder that she has had all along and it has finally been revealed. Good luck!!!