Remoraze and Banishment

Our wizard was down to her last few hit points after being swallowed by a Remoraz. She wants to cast banishment with the intent that the Remoraz will be banished but she will remain behind. We ran out of time and ended the play so I wanted to get your feedback. My thought is that she would be banished too since she is inside the monster same as anything else it ate, is digesting etc. I'm going to suggest she use a reaction to ponder real quick if this is indeed the best course of action vs a kick ass spell. Thank you

TLDR: does someone swalled by a Remoraz become banished too with the banishment spell or do they stay behind.