Is there a way to merge emails from one Office 365 account into another?

Long story short, when a staff member has a name change, we have to create a new AD account due to how the account ties into other applications. To do this we apply an Office license to the new account so the staff member can log into the new account and use emails under the new name. However, their old account is still out there so they are eating up two licenses for the purpose of going into their old emails until they migrate everything manually to the new mailbox. This technically works, but it causes a lot of time for the employee to move things over and is another thing we have to remember to shut off in the future. So let's say Sarah Jones is now Sarah Smith. Sarah Smith logs into her new AD account with the same groups and permissions ans Sarah Jones and has a mailbox for Sarah Smith, but she also has full permissions to Sarah Jones mailbox to compare and create all the folders and copy emails into Sarah Smith mailbox. Is there a way to just migrate all of the email folder and contents from Sarah Jones to Sarah Smith without this manual process? If this can be done, then we can also shut off the old Office license when Sarah Smith logs in because emails are the only reason it is still active.