I would recommend camille file i-130 as a petitioner. Wait for the application to get approved, later when nvc ask you to pay fees, visa fee and Affidavit of support fee, you pay as a petitioner from ur account. Aunt can transfer you money to ur account to pay the fees. For actual affidavit of support, camille will fill 1 affidavit of support, i864 as a petitioner and aunti will fill one as joint sponsor.