She doesn't say "What." again because she has more dignity than that. But a small part of her does think it.

"What would it mean for me to have a ... pure gallbladder?"

"It would mean that having an untainted gallbladder is the anchor of your powers! If something ever caused your gallbladder to become impure, you would lose your empowerment."

She's read that microplastic contamination studies are methodologically flawed, but it's probably better not to chance it. She's also not sure what a small gallbladder would do to her.

"What about my gallbladder being secret? What does that entail?"

"You'd have to keep the fact that you have a gallbladder secret from people. They would be allowed to suspect, on priors, but you would have to avoid ever admitting to it, or referencing it, or letting them see it for themselves."

If her gallbladder is too small, she'll have to deal with a medical problem of some kind, probably. If it's pure, she has to worry about environmental contamination. If it's radioactive, she'll have to deal with cancer of the gallbladder, which sounds bad. If her gallbladder is temporally displaced, she'll get headaches. Not because of the operation of her gallbladder, but because time-travel shenanigans give her headaches and apparently PMMM was a documentary.

So.

She can avoid admitting to ever having a gallbladder. It's not like it comes up frequently in conversation. 

"Secret, please."

"Excellent. That's the final question, so are you ready to lock everything in? Your endorsed qualities (in full generality) will be as the endorsed qualities of ten, because your gallbladder is secret?"

"Yes. Do it."

There's a flash of light. But it's more 'suddenly turning on the old lamp in the livingroom' and less 'brilliant flash of reality-redefining luminescence'. Sarah gets the impulse to stand and do a spin, and when she's done, her shoelace is untied.

"That's it?"

She blinks at Kyubey, nonplussed.

"This way's a lot less efficient! But we make it up in volume," Kyubey agrees over its shoulder, already trotting away to intercept a jogger in violently green leggings. "Enjoy your endorsed qualities! Hey, you — your species has free will; will you make some choices for me in exchange for magic power?"

After a long minute, she heads home. Somehow, she is perfectly punctual. She makes a cup of tea, and it is extremely relaxing. When her partner gets home from work, she explains what has happened — about ten times more eloquently, if she had to judge.

And that night? Well, her ability to get a good night's rest is an endorsed quality too.