I hope BellaDonna returns, but this does give some more of an explanation. I think you should have been informed about her adoption status.

At least knowing she's not a pure indoor helps!

only rarely gives out barn buddies, with the caveat that they should be prevented from getting out of the barn for a month or two (I think that's the time frame). Even if they're feral, by month two they will be generally happy to stick around for a free meal and good hunting, returning to the barn for shelter and food. They'll consider that "their" territory in that period of time.

Some lady adopted three or four barn buddies a few months ago. I imagine they're doing well.
That sucks, I'm sorry to hear about this.

From December 26 until mid-March. It was only in the last week or two, when the weather got warmer, that she started venturing out at all. And only in the last week that she started pulling all-nighters. Twice she stayed out all night and returned to sleep in the next day. The third time was last Thursday night.

That's pretty unusual from what I've gathered.
She may be closer than you think. We used to take care of this feral cat that would vanish for weeks on end, and then turn up looking as us like "What, you were looking for me?"

I'm sorry for you. That stinks.

Cats have long memories. Yes, some prefer to be wild, but if she needs shelter and food she'll know where to find it.

But it's possible the shelter thought she'd do better in a home...maybe she wasn't feral enough to be a barn buddy. That may be it.

But you gave her a good home for the time she was with you. And if she returns, well, then she'll return.

Are you going to try to get another kitty? I always believe the right one will come along. I waited quite a while to find the right companion for my dog Rosie. I tried overnight stays, and one week long babysit, with different dogs. They weren't quite right. But we finally found the right companion for Rosie (actually, Rosie picked him out at a meet and greet at Petsmart...I wasn't going to look at the one we got, and I wasn't interested in him...but Rosie fell in love with him. It was love, if ever I saw it. She only had eyes for him. We brought him home for an overnight stay to see how it would work out. He's still here, several years later. Rosie and I love him. He wouldn't work out just anywhere...but he's right for us.)