Single user with multiple accounts

I would like to add the instagram feed for a user who runs multiple accounts out of one login. Basically the user is our school principal who has a personal account as well as a secondary account for the school on that same login. When I authenticate with her credentials I see just her primary instagram account and there does not seem to be an option to select the secondary account.

My initial idea create a secondary account specific hashtag that she would use each time she posts to the secondary account and setup a filter to only show those posts. Is that the only way to achieve this? Or is there an easier way?