What a wonderful friend you are! Explain to your friend that she is depressed and has every right to be, she has been thru an awful lot. Tell her that some things in life are just too big for us to handle on our own, and she needs the care of a professional. Tell her to think of everyone who loves her, and how her dying would affect them. Tell her it's not her time, and suicide does not mean the end of it for her, and it may be worse. If you feel that she may be able to have another baby one day use that also. You know her best, just think of what will motivate her to get help. Make sure she knows that suicide is not the end.
Best to encourage her to see a psychiatrist. As well having a micarriage can be traumatic for any woman (I had a family member go through that) and there are support groups for that as well which might be helpful.