OMGGGGG, BBABBYYY, TODAY IS YOUR DAY. YOU'RE FINALLY GONNA BE ( her age.). I LOVE U SO SO MUCH AND I REALLY HOPE U ENJOY YOUR BIRTHDAY. YOU'VE ALWAYS BEEN NEXT TO ME AND I AM SO GRATEFUL TO HAVE A TWIN (BEST FRIEND) LIKE YOU (heart Emojis). ONCE MORE, ENJOY YOUR BIRTHDAY TO THE MAX. but Don't enjoy it too much without me (laughing hard emoji and heart emoji)
I would probably say something that tells her how important she is to you and how much you appreciate her friendship. Make sure that she feels special. Ex. Hey! Thanks for being such a great friend (and twin!) I really appreciate you and I hope that you have a GREAT birthday!
Ex. Hey! Happy birthday to my best friend/twin. I can't express how much you mean to me and how much I appreciate how you are always there for me no matter what. I don't know what I would do without you. Have a happy birthday!
This is a SIMILE - if words such as 'as' or 'like' are used in order to compare two things (in this case, 'giant rocks with razor edges crouch LIKE a sea monster with wide open jaws'), then it is a simile.