Hello, Thank you for using Justanswer.com. I am sorry to hear your daughter is going through this. When someone is depressed it is very hard for them to see what is happening to them.
Unfortunately, there is very little you can do to help a person in this situation. Sometimes, you have to wait until you believe people are actually suicidal before you can enlist outside help to get her help.
I'm thinking since she is already angry and distant from you, you may want to consider (if you haven't already) talking with health visitor about your concerns. The health visitor may be able to require her to take her son for help and sometimes require her to get an assessment for herself. If that intervention doesn't help, all you can do is gently express your love for her and that you are there to help her if she changes her mind and asks for help.
You are doing one very positive thing and that is reaching out to someone else (her partner's mother) for support. This type of pain is hard to endure by yourself. I would also suggest seeking a therapist to help you with the sadness and worry you are feeling. Unfortunately, we do not have control over others and how they want to live their lives and you may need to let go for now with the hope that she will get the helps she needs when she is ready to accept she has a problem.
Lastly, here is a good online support group for family member who can not directly help their loved ones.
I wish you all the best with this problem. Please let me know if you need further clarification about this answer.
All the best,
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