I agree, it's best to get her to a vet.
That said.... our Flowerbelle is small and thin. She always looks bony and too thin. However, as she's gotten older, she's developed a problem with hairballs. It's not that she eats too fast, it's that she gets a belly full of hairballs, she eats, the dry food expands, and she throws it up undigested. If she hasn't been hacking, this is how we know she needs hairball stuff. She hates it all, and we have to get that ribbon of crap down her like a med.
I don't know if this could be part of your kitty's problem or not.
But if it were us, we'd get another blood panel to make sure there's not a thyroid/kidney/liver problem.
We'd give her hairball meds. This is the stuff we use: http://www.petsmart.com/product/inde...ductId=2751724
ALL of the other cats love it and just lick it out of a bowl.
And I'd feed her kitten food (if the vet says there's nothing wrong with her).