Looking For Niece (Laguna Niguel California)

Hello, I'm looking for my biological niece.
Her birthday is around June, July, August years 1998-1999 ? my sister and niece "biological mother" arranged for an open adoption though Memorial Hospital in Long Beach, California, where her daughter was born.
after 3 or so day later she was put up for adopted.
Since it's was an open adoption the adopted parents was there.
My nephew, "biological brother" and family been looking for her on & off for years, as she is his only immediate family left for her brother.
This is what I know about the adopted family the mother was / is a surgical nurse her name might be Allysin " might be spell different" and the dad sold cars in Laguna Niguel California, his name might be John,.
I have photos of the birth mother and family, also the adoptive family… along with both bother & sister playing together.
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Her name might be Katie / Catherine to confirm this.
We would so appreciate / welcome If anyone having any information that will help us find her please contact me.
❤️ Thank you Auntie