Maybe a neighbor popped a mole in his yard with a .22 and a local cat brought the offering to Abbey, since she can’t get out to hunt herself.
That’s rather why I’m thinking ‘cat who has a human-provided food supply.’
Maybe another cat came through and caught the mole, and that’s what got Abbey interested in getting out there?
It’s been a while since the last Kitty Report, but this is new.
Abbey likes to hide sometimes. The other day I went all over the house looking for her and calling her. Here’s the thing: Goo helped. She got off the bed and followed me around to help me look for Abbey. Tonight she helped Catmom look for her. It’s so cute!
I once succeeded in finding a hiding cat only because another cat was looking very intently at the space in which he was hiding.
(It was another of those ‘a cat couldn’t possibly fit in there’ spaces. Yes, they can.)
I’m sure Goo knows exactly where she is. But she seems to like to help us look for her.
Maybe she thinks you’re just taking a roundabout path to wherever the treats are. 
Yeah, zombie thread; but better than starting a new thread.
Abbey was timid when we got her. She didn’t want to go out into the catio. I’d pick her up and take her our for a ‘tour’. Catmom would tell me not to upset her. Now, Abbey likes to go into the catio.
I used to try to pick her up and put her on my lap when I was on the couch. She’d say, ‘No, no! Don’t hold me on your lap! Let me go!’ Now she crawls onto my lap on her own accord.
She’s such a sweetie. 
Goo still won’t get into my lap. But she’s been more generous offering me her belly when I wake up in the middle of the night. 
Congratulations on getting Abbey to trust you so well! as well as to trust the outside.
And for that matter Goo; allowing belly rubs is definitely a gesture of trust, even if she’s not a lap-sitter. One of mine is like that.
And thanks for the update.
So, yeah. We adopted four-month-old Findus. It’s only been five days. Neither Goo nor Abbey like him. Abbey growls, and Goo hisses. But Findus is a brave little boy. Today, Goo was in the short tree by the front window. There’s a ‘pedestal’ (carpeted cylinder with an inside space) next to the short tree. Findus got on top of the pedestal, and sharpened his claws on the upright that holds the top of the tree. Goo just looked down at him. She may have hissed at him, but I don’t remember. At dinner time, Abbey was on top of the short tree. Findus plopped down on the floor near to where I was preparing their dishes. Goo did the rubbing-on-the-leg thing, where she says, ‘I love you dad! Please give me my gooshy food!’ On each pass, she hissed at Findus. But she was more interested in rubbing my leg in anticipation of dinner. Abbey stayed in the short tree until I took Findus’s dish back to CatMom’s room.
Findus is in bed with CatMom. I don’t know where Goo is at the moment, but she’ll sleep with me. Abbey is on the other end of the couch from me, laying like a meatloaf, the big sausage. Oh, there’s Goo. Looks like she wants to play.
What a beautiful kitten!
And if you can have them all in the same room after only five days, this will definitely work out.
Thus the birth of the term, “catty”. LOL
Kudos for your patience and methodology! They’re both lucky to have you! 
Can you believe the OP was over four years ago? I wish Abbey would remember when she was the newcomer!
Findus ventures out, which is good. Goo hissed at him. Abbey’s out in the catio, in the cold.
Additional: Findus came to the edge of the living room, and Goo hissed. I got up to tell her it’s OK, and she headed off to CatMom’s room. At the other end of the kitchen, Findus ran and overtook Goo… earning another hiss, and the first swipe I’ve seen Goo take at her. A minute ago, it looked like Findus was following Goo around. Haven’t heard any more hissing yet.
In the cold? Is she making a statement? 
No, she spends most of her time in the catio. It’s just not cold enough for her to want to stay inside.
Findus is trying to make friends. And will probably eventually succeed, though it may take a while.
Long I or short? Is the name because she found you?
Yes, he really wants to make friends with Goo. Abbey, too; but she stays in the catio and he’s too small to be let out there.
Short I. In the stories, Findus got his name because he was in Findus Green Peas box.
Findus got a swat today. I shredded the rest of the cheddar, and there are always bits. I gave some to Goo, and to Findus who was a foot and a half away. Goo finished hers, so I gave her some more. The Findus finished and started advancing and sniffing in Goo’s direction. Goo hissed and swatted, ‘Oh, no you don’t!’
At diner time I forgot to shut the door to CatMom’s room, where I fed Findus. He finished before Abbey did, and scared her off. I ushered him back to the room and shut the door. Abbey went to the French doors (to the catio), wanting out. I picked her up and took her back to her dish, but she didn’t want anymore gooshy fud. (We give Abbey ⅛ of a can, and she almost never finishes it.) She left about half of her portion, so I opened the bedroom door and Findus cleaned up what she didn’t eat.
Yesterday Findus was playing with the water in the water fountain. Goo crept up behind him and sniffed the base of his tail. Of course Findus looked around. Goo hissed at him and backed off. Repeat twice more. Goo still hisses at Findus, but I find it encouraging that she’s showing curiosity.
Findus is under the coffee table right now. Abbey is sitting on top of the coffee table, right where I keep my work computer. (My work computer is on my lap right now, since I’m working.) Abbey is just growling at Findus. And… she’s gotten down. She growled a couple of time crossing the four or five feet to the catio doors. She’s meowing to be let out.
Abbey is not a happy kitty. When she’s not growling at Findus, she’s crying. Let her out in the catio, and she cries. Let her inside, and she cries.
Findus is lounging on the back of CatMom’s chair. (She’s out seeing a patient.) Goo is curled up asleep in the cat tree. I went out into the catio with Abbey and put my feet up on an ottoman. Abbey came across the leg bridge and got pets and scritches for about 10 or 15 minutes. I think we’re friends again. She went to the other chair by the table, and then curled up in my chair when I came inside. Forty minutes until gooshy food.