since you have the courage on this, then y not give her a sms
first?
if she asks about how did you get her number, maybe u can try
something like mentioning about her absence in office and you've
found out recently that she had resigned. Hoping to meet her again,
you went through may ways to get her number.
jus sms her lah, it's better than u regret in the future. i had a
similar case like this, 8 years, still...the feeling is damn f**ked
up.