🚀 go-pugleaf

All the "conning kitty to eat" ideas are good, but be sure that
there isn't something else wrong.  A "cold" in kittens may turn out to be
neumenitis (kitty pneumonia) or distemper.  Just because the other kitten got
better doesn't mean this one doesn't have something serious.

Take her to a vet you trust PRONTO 

If it IS just a cold, food should help - kittens don't have a lot of body
reserves to live off of.  Especially try to force water (even sugar water if
she won't take food)  - a turkey baster makes this pretty easy.  

When a stray kitten we'd picked up had distemper, we finally got her to eat
cottage cheese and egg yolks (and she made it!)

One final word on selecting a healthy kitten (or puppy):  young animals are
pretty active unless they're asleep.  If kitty just lies there doing nothing,
chances are something's wrong (probably just worms though).

Good luck