Now that does actually surprise me!

 She said she can speak like a native ..not write like one ...

 Why?

this actually reminded me of a part from pink panther the movie

http://www.youtube.com/watch?v=0BFh90GTFOM

Because I thought you were a native speaker of course!

 Shall I make some mistakes to prove I´m not?

I like the one where Joey from Friends is trying to speak French - it is like the other side to the video you posted.  Unfortunately, I can´t seem to get the link - so Trudy is going to add it for me!  Thanks Trudy

 Here it is:

http://www.youtube.com/watch?v=DqwzvtjeYBQ

I hope you can open it.

Henry Piaget answers your question, he proposed that there is a special phase in a childs mental development where the brain accords itself to the wovel positions, fundamental syntactic rules and a set of other properties specific to one´s own native language. Once this language acquisition window is closed it may be virtually impossible for an individual to truely acquire a language. Bilingualism or trilingualism is possible in practice but in reality no matter how many languages one can speak, only one of them is his/her native language. It is generally accepted that the language that you do the calculations with is your native one.

Unless, you are giving up your identity or thinking of working as a spy in another country, don´t ever think of becoming a native speaker.  There are a lot more to add on top of the mastery one gains in the early years of life. These include local dialects, thinking patterns, accents, jargons and slang...