Lilibet was her nickname since early childhood when she couldn’t properly say her name. So much gossip about the royals I don’t know if she was happy about it or not. But I don’t think it was done with malice.
My family called me “ab” for the same reason.
You are correct, Lilibet is the nickname she gave herself as a child.
That’s what I get for listening to the LSM who were speculating whether Harry got permission to name his daughter that as it was the nickname Phillip had given her and what he called her.
They don’t know their facts, now do they?