Sponsor student visa

I'm applying for Italian student visa and my dad has retired last year, he can't fund my education but my sister can. Is my sister eligible to sponsor me?

I emailed vfs and they said only parents, spouse or child can sponsor me but another friend of mine was sponsored by her brother.

I still have 3 months to apply for visa, my sister can make my bank statement but will they ask for proof of income that where did money come from in my account or is that a good idea? or is my sister bank statement will work for me?

On side note, I'm from pakistan born and brought up and currently living in dubai. My sister current balance is around 20k$