http://www.reunion.com is a possibility for people that want to be found (for things like school reunions). Google search on her name might work if it really is uncommon. Of course this only finds things she might have on the web (like a web sight or newsgroup postings using her real name). Finally if you are desperate and willing to spend some money there are professionals who will search for you for a fee (several hundred dollars) though I have no idea if this is any better than searches you could conduct yourself. Some libraries have old phone books in their archives, you might be able to find a listing for her from 1990 which might give a address to start with, for example.