Please, help me to write birthday wishes on Japanese!
Hello! Today is my friend's birthday. She likes Japanese culture very much, she have been to Japan and she speaks Japanese, so I want to write her a happy birthday wishes on Japanese! But I can't speak or write on this language at all.
Please, help me to write something nice
Great thanks, Mary

Question

Please, help me to write birthday wishes on Japanese!
Hello! Today is my friend's birthday. She likes Japanese culture very much, she have been to Japan and she speaks Japanese, so I want to write her a happy birthday wishes on Japanese! But I can't speak or write on this language at all. 
Please, help me to write something nice
Great thanks, Mary

Answer

Hello:) The most simple way is that : おたんじょうび　おめでとう！(Happy birthday!)

And if you wanna put something more, I give you more examples!

すてきな　いちにちを　have a great day

よい　いちねんを！I wish you have a nice year

まりいより、あいをこめて  with love, Mary

I wish her a Happy birthday from other side of the world!

Answer

「お誕生日おめでとう！いつまでも友達でいましょう。」
（Happy Birthday! Let's be friends forever!.）