So sad
But it sounds like you did everything you could to find her.
Hugs
How I did it: She was here one day, and gone the next. She did not appear to be ill. We put up notices, we called the vets and the animal shelters, I entered details on a 'missing pets' website.
All to no avail. We have no idea at all about where mother cat is, or if she met an untimely end somehow.
Cora_and_Clarice is getting her head out of her ass
My heart goes out to you and yours.