Je suis une alouette means 'I am a skylark' in French.
je suis une étoile means 'I am a star' in French.
"je suis une dolly" means "I am a 'dolly'". Dolly is an English word, not French.
I am a girl.
"I am in a..." It's not a complete sentence.
"I am a wonderful girl."
Je suis une fille
I am a potato
I am a child (it should be - un enfant)
I'm a box of kisses
"je suis un ... / je suis une..."
'je suis' means I am (not j'ai suis) and 'une soeur' means a sister (NB 'une' as sister is feminine)