I meet her mother during my vacation and have a one night stand. I came back to North America and lost contact with the mother as I have meet another woman who I am currently living with (that was 20 years ago). To make the long story short, I was tracked by my daughter through Facebook. She told me that she was given up for adoption but her adopted mother has now passed away. Her biological mother has a family on her own.
I want to sponsor her to North America. The problem is, I don't see my name as the biological father on her Birth Certificate? Because of this, can I still sponsor her? Do I need a lawyer? A possible DNA test?
Please advise.
Thanks!

Without a doubt you need DNA testing - and an Attorney.