Just hang around her work, and follow her home after a shift. Or if you can narrow it down to a specific area, then pay the local kids to find her for you.
That way, when you decide to go all Raoul Moat on her ass, there will be loads of people who can sell their stories.
BTW is this your first time stalking, or is it something you do a lot of?
If she is on the electoral roll, you can go into your town library and ask to look at it, it is however usually in ward order in the library format and so you would need to have a rough idea what streets she lived around about.
Do you know anyone who may know more about her?
Bev........if it's a small town lots of people will know where she lives so just ask one of them
Although I get the impression you want to send her a letter she might not want to receive?......like an anonymous one telling her her husband/boyfriend is cheating on her?