Skinny but attractive girl, about a hundred pounds (7)
I believe the answer is:
cuticle
'skinny but' is the definition.
I can't tell whether this definition defines the answer.
'attractive girl about a hundred pounds' is the wordplay.
'attractive girl' becomes 'cutie' (cutie can mean an attractive person).
'about' means one lot of letters goes inside another.
'a hundred' becomes 'C' (Roman numeral).
'pounds' becomes 'L' (abbreviation e.g. Lsd - pounds, shillings, pence).
'c'+'l'='cl'
'cutie' placed around 'cl' is 'CUTICLE'.
Can you help me to learn more?
(Other definitions for cuticle that I've seen before include "finger has one" , "Protective layer" , "layer of protection" , "Dead skin at the base of a fingernail" , "Skin at foot of nail" .)