Don't give up on the friendship, but have several topics of conversation ready if she commences another misery monologue, and be resolute. If she still continues, (you know how much time you are prepared to give) then gradually ease out of the relationship. Some people feed on the sympathy and don't try to move forward.
I can't say have met anyone like that, and I have a few friends whose husbands died before their time, or divorced them, leaving them with younger children, mortgages and bills to pay. They simply got on with life because they had no option, suffering bouts of grief but always attempting to look forward.