Okay, let's start from what's wrong with her.
You knuffel doesn't evolve between stages. Almost not at all. There should be
3 big changes between stages. Things like earrings, small ribbon on top, small shoes, bracelets etc don't make big changes. Please consider Firn checks overall knuffel evolution in around 17% of their original size. Small elements won't be even visable.
I don't really think knuffel should be totally naked in 1, it makes it appeal less, but let's say it's okay. You have 3 big changes between stage 1 and 2 (top, pants, tail), 2 big changes between 2 and 3 (top, ribbon), 1 big change between 3 and 4 (wings, guess skin color could be second one though it's hardly visable at first sight) and 2 big changes between 4 and 5 (ribbon, wings, guess hair getting lighter parts could be counted too). There are small changes in hair lenght between stages, but change should be visable right away, not after few seconds of staring at knuffel and searching for it.
Whatever you draw on her stays pretty much the same till the end, while elements on knuffel should change and evolve at least a bit between stages. You drew tail in 2 and it is the same till the end. Top parts are same starting from 3. It's hard to call it evolution :<
I'll give you basic example on how you could redesign her and what changes you could do to make her actually acceptable. Sketch is really derpy, but it's way too late for me to do a good one. Just analyse those examples:
http://i.imgur.com/QLeJ1.png . Not saying that's how she should look, just a basic idea on how you can design/switch elements to make them change more.
Changes:
s1: short hair, basic bra and panties
s2: Bigger: hair get longer, panties turn into short pants, bra turns into simple white top Smaller: shoes
s3: Bigger: hair get very long, ribbon on hair, red blouse on top, small fairy wings without pattern
s4: Bigger: wings get big but without pattern, gets short tail Lots of smaller: ribbon gets hairband, bracelets on hands and earrings (forgot to draw 8) ) and short socks in color of top
s5: Bigger: white fishnet on ribbon, big wings with pattern, long tail, Smaller: ribbon on shirt
You could also consider other elements, like red bangs in hair in last stage to make them stand out more etc.
Btw. she has ears on different levels in each stage. It's kind of strange O.o