you know , it is quite possible your ex has tiold your daughter you are dead and she has spent her life depressed that she has never met you.
Your ex hid / threw out the presents and cards to ensure that the idea of you not being around was concrete for your daughter.
it is quite possible your ex told your daughter that you would be back some day , while secretly chanigng her INFO so you CANT find her, and watching the tourment it is causing your daughter.
a simple 2 sentance letter will tell her you are still there, and give her the opportunity to contact you with out disrupting her life.
She knows about you. It is impossible for her not to. You last saw her when she was 3 ?
Yeah, she remembers. Absolutly.
Offering for her to know you wont damage her life in anyway.
Now, showing up on her dorostep, ... well.. that might.
I think a letter gives her , her privacy, isnt intruding on her perception of you ( unless she thinks you are dead) and gives her a chance to decide for herself, something she has not been able to do , if she wants communication with you.
Right now, you not having communication with her is not 100% her doing.
This is your ex's doing.
I say write her and give her a chance to make up her own mind..
but then again.. the question still comes down to
HOW