Wow. Donor eggs are done so differently here in nz. And I'm so fortunate that we do do it differently.
I'm an egg donor. 4 times, 1 successful. For each donation, I met the recipient couple, talked with them, talked about their lives our lives, the upbringing of the hopeful child. What kind of parents they would be. Etc.
We all agreed on open donations - there was never a question of telling the child. And from the one successful donation I get letters, emails, photos. We've stayed with them (they don't live in the same city), and they are coming here next year.
The child understands (she's now 10) who she is, how she came to be, and has her own description of who I am. For me, they are my extended family. Mum is like my older sister, the kids (she had one previous) are my nieces.
I believe that in Europe, egg donors are paid for their eggs, however in nz, they are voluntarily given. In nz, there is an addendum on their birth cert which notes her genetic link to me.
I'm trying not to be judgemental of you OP. I don't see what you would lose by being open with the child. I can only see that you have so much to gain. No one will judge either you, your family or the child.
For me, I was in a position to help someone who couldn't achieve what they wanted on their own. and I'm forever grateful that I gained such a loving family from my one gift.