Meeting invites going to wrong mailbox

Hello,

My colleague has two mailboxes:

- "Mailbox A" = Her primary email account (e.g. *** Email address is removed for privacy ***)

- "Mailbox B" = A generic account for a specific purpose (e.g. *** Email address is removed for privacy ***)

All of the email she sends and receives for her day-to-day work is done through "Mailbox A", which is perfect! 

If I sent a meeting invite to *** Email address is removed for privacy ***. it shows up in Mailbox B (*** Email address is removed for privacy ***). 

How do I have these meeting invites show up in Mailbox A?

Thank you!