You have to help her move on. Get a new girlfriend.
She is currently undergoing a grieving process, here:
http://en.wikipedia.org/wiki/Grief It appears that she is in the Shock and Denial stage. Eventually, you'll need to facilitate the Despair and Depression stage to help her recover and move on.
Grief due to the death of a loved one is no different from grief due to the parting of ways of people in love. Some people can move on faster than others.
To prevent any stalking from your ex in the future, give her a token gift, say, a Parker pen or a chain watch. This token item will help cushion the pain and stop any of her impulses to stalk you.

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Approach. Open. Escalate. Isolate
Here are my two essential rules on texting that will save you tons of time and money:
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