Hi,
According to your description, I understand that a meeting forward notification will send to her boos when she create a meeting request on her boss calendar, she is a delegate to the calendar of her boss.
If I misunderstand your concern, please do not hesitate to let me know.
Basis on Microsoft document, Outlook sends a meeting forward notification to the meeting organizer when you use Outlook to forward a meeting to someone that was not originally invited to the meeting. The prerequisite of meeting forward notification is existed
meeting request, therefore its not possible happened as you mentioned.
For your question, I want to double confirm what has she done before issue occur, for example Outlook update. Whether all account or only one use experience this issue. Please try to create a test mailbox and deploy delegate access to reproduce this problem.
If this only occur on one account, then make sure which side caused this issue, the setting of her bosss mailbox or her own mailbox. Try to configure delegate access permission to another mailbox, then check the results.
As my experience, we can check inbox rule, delegate access permission and Outlook virus and add-ins.
Best Regards,
Allen Wang