Hi and Welcome 😊
People who are not feeling well (either physically or emotionally) have a tendency to lash out and behave in a manner which is not appropriate, and can be hurtful to those close to them. It's normal. When somebody says something hurtful or behaves in a manner that is out-of-character and not nice, it is indeed a warning sign that they are struggling and under severe stress. As a good friend it is important to allow this to happen and to try not to take anything said personally .... even though this may be hard at the time due to your own vulnerabilities.
People in general have a hard time fessing up that they are struggling emotionally. We live in an age where we have fundamentally been conditioned into suppressing our emotions and maintaining a facade of health and well-being. It takes a very brave person to actually speak out about how they are really feeling internally. As a good friend it would be great if you could speak directly with her about her behaviour and to ask what is really going on for her. Truthfulness and honesty when conveying feelings is a two way street. Perhaps if you talk openly about the not-so-good things happening for you, this will make her feel more at ease to share her feelings with you. At some point you need to let her know that what she says hurts you, but also assure her that you are there to listen to her in a non-judgmental way.
If you believe that she is suffering with a mental health illness you need to view this as you would any other illness of the physical variety. There really is no difference, other than one being physically based and the other being psychologically based. One may be seen, or validated via tests, while the other is unseen and not able to be validated easily.
It's really important to keep your boundaries in place. Tell her up front that you are there for her as a friend, but that you need to draw the line in the sand when it comes to her saying nasty and hurtful things. Not because you don't like her or want to end the friendship, but because you are trying to protect yourself emotionally. If you feel for whatever reason that your continuing friendship is significantly compromising your own well-being then it may be wise to distance yourself from her, but not before you advise her of what you are doing and why.
I feel that you need to talk openly with her about the exact concerns and issues you've raised here. Tell her that you are concerned for her mental well-being. Tell her that you are questioning your friendship because of her behaviour. Give her the opportunity to hear you and take/make corrective measures.
I guess this boils down to how much you value your friendship with her. The very fact that you have posted here implies that you do value it, and that you are anguishing over what to do, rather than just abandoning the entire friendship. It's a sign of emotional maturity on your behalf to take the time to consider her, you, and to consult others, before making any major decisions.
I believe there is nothing more postively powerful than to have the love, understanding, tolerance and compassion of another human being.
"A true friend is someone that sees the pain in your eyes while everyone else believes the smile on your face". 🌹
Hope this has been useful. All the best.
Janna ❤️