How About You Just Rip My Heart Out, Instead?

As most of you know, we foster dogs for a rescue group. We've done very well about not getting attached to the dogs, for the most part. In fact, the only foster dog we've kept is one that Dysfunctional Dad got attached to. It wasn't my fault! Other than him, we've been able to take these dogs, help them get healthy (in some cases, take them to heartworm treatments, have major dental work, etc), and then lovingly pass them on to forever homes.
Back a couple of months ago, I got an urgent call from a rescue member, asking me if I could pull a dog from my county shelter that day or she'd be euthanized. I got the message too late to go that day, and I panicked; but fortunately she'd talked them in to waiting until the next day. So first thing the next morning, I picked up Suzie.
Suzie was skin and bones, and had liquid poops. She was in terrible shape.
We took her to the vet, and treated her for whipworms, which were causing her bowel problems and her inability to put on weight. She now looks and feels so much better. But she's still very old, around 14 years old. She's frail. And she's very, very attached to me. She sleeps right next to me. She follows me everywhere. She doesn't care about any other person or dog; just me.
Just last week, I said to hubby, I think we are going to have to keep Suzie.
She probably doesn't have a whole lot of time left on this earth, and I don't really know how she'd handle leaving our home at this point. Hubby agreed with me ('cause he's awesome like that).
The only issue is her adoption fee; while it's not much at all really, every dollar right now is going to the down payment for the Ladybug's braces. But I figured, well, nobody's showed any interest in her so far, so we'll probably have time, after we get the braces out of the way next month, to get the adoption fee paid.
What I didn't know was that the rescue group hadn't gotten her bio up on the website yet. But just this week, they put Suzie's bio on the website. And already, TWO people have shown an interest in her.
Oh.Crap.
I know the rescue group would hold her if I asked them to. But I'm so torn. I want what's best for Suzie. What if these people would give her a happy, comfortable forever home? I try SO hard to remember that we are fostering these dogs, and the goal is to let them go. And I've never had a problem with that.
Until Suzie.
I just don't know if they'd understand her. One of them said they're looking for a companion for their other dog. Suzie doesn't hang out with other dogs. Suzie likes people. (Suzie likes ME.)
The other one asked if she plays with toys. Suzie mostly sleeps. She wakes up to eat and go outside. She's not into toys. She's not into playing. She's a feeble old lady. And I love her.
I just want what's best for Suzie, and I want to do the right thing as a foster.
Why does it have to be so hard?


Here's a puppy picture for your viewing pleasure. This is Spikes, the 8 week old pupster. Apparently he likes to sleep while inhaling the lovely aroma of Dysfunctional Dad's toejam.