Your girlfriend has been through a shock. Even though she left her ex, she did love him once enough to marry him. It is normal for her to need some space to come to closure about her marriage and to grieve the man. It would not be unusual for her to be going through thoughts about what she could have or should have done to help her ex. It’s unlikely that anything she might have done would have changed what happened. But people often do go through a period of self-reflection and sometimes even self-blame when there’s been a tragedy. Usually it just takes time for someone to get their bearings and to move on.
I think you should take it as a positive comment on your relationship with her that she is wearing jewelry you gave her. It may be the best way she can reassure you that her love for you haven’t changed; that she just needs to take a step back to sort out her very complicated feelings.
You’ve only known each other for 6 months. Your girlfriend hadn’t finished her divorce when this happened. She’s going to need time to heal from both the marriage and the death. What she needs from you now is loving support and no pressure. If she can’t seem to pull herself out of her grief after a few months, she might find it helpful to see a grief counselor You could even offer to go with her in order to learn how best to support her.
You have a lifetime ahead to be with her. Slow down. Put her needs ahead of yours for a while.
I wish you well.