Airtable payments are per person per workspace, not per account.
Does your boss already have an Airtable account and workspace? Does you and your boss need to be able to work on the same bases? Does your current account contain work bases, personal bases, or a mixture of both?
If you and your boss need to work on the same bases, your boss can upgrade her workspace, and invite you as a collaborator on her workspace. She would be responsible for paying for both users in her workspace. Any bases in your current free workspace would be unaffected and would still be limited to free features.
If you need a plus account but your boss does not need any access to the data, it may be simpler for you to expense the cost of an upgraded workspace and have your boss reimburse you.
An Enterprise workspace would not make sense for two people who only need plus features.