Ownership of a business Instagram account in a dispute usually depends on who created it, who has controlled the login over time, and what the parties agreed in writing. Instagram's Terms of Use say you can't buy, sell, or transfer any aspect of your account, so a sale or separation agreement rarely transfers the account on its own. Attorneys typically look at the records to decide who controlled it and what the loss is worth.
Accounts get built over years by one person, then the business is sold, the founder leaves, or an agency relationship ends. The account holds the audience, the content, and often the bookings. Nobody wrote down who owns it.
Not by itself. Because the Terms of Use bar transferring any aspect of an account, the practical question is who holds the credentials and what happened when control changed. That is why a records-based timeline matters more than the wording of the sale.
Valuation is a separate question from ownership. I wrote about the method in "What Is an Instagram Account Worth in a Dispute?" In short: rebuild cost, bookings attributable to the account, and engagement.
A social media expert can build the control timeline from platform records, explain what the data shows, and separate platform facts from the legal conclusion that belongs to counsel. I work with attorneys on these questions. To request my CV and fee schedule, see my social media expert witness page.