I am 35yo and a few days ago I found out that I was a father to a 16yo girl... the mother made contact with me and sent me photos, she told me that my daughter believes another man is her father... She said she thought it was time I knew the truth, she even asked if I would like to make contact, but she has now changed her mind... and wants me to be someone she(The Mother) can talk to online but under no circumstances am I to make contact with her... I do not have any other children as I only ever wanted them with one person(Her). She and her family moved away, v quickly... I now know why...
I feel like I've been shown a fantastic view of the most wonderful part of my life... only to hv it snatched away...
Why has she after so long, told me about my daughter... Am I being selfish to want to make contact, it would turn her life upside down... But on the other hand shouldn't she know the truth, it appears that she is actually friends with my niece... and I'm scared she could find out from someone else. Im in so much shock about this... I want to know her, but I want her to be happy... what should I do?

Sounds like a bit of psychosis going on with mom.
Here is the bait, got you hooked now keep you for my own online toy. To talk to and torment?

You may have a rough road ahead of you to contact your daughter.
Also thinking of her, and she is believing another man is her father is a matter to be handled with kid gloves
It could turn her life upside down . Or not.

If your niece is friends with her I would casually try to gather some information about her and her family.

I would be hesitant to believe much from the mother. She obviously has her own agenda.

I would consider hiring a PI to gather some backround which may help you in how to approach this.

But gently and cautious be the way for now. Good Luck