Can you edit an outlook calendar invite you didn't create

I have a user that wants to add information to the subject line of a calendar invite she didn't not create. Any suggestions?

That depends on the situation. The question was not specific enough to answer it easily, but luckily there aren't many flavors, so answering all conditions is not too much in this case.

A meeting can be changed by the following people:

• The person who hosts the meeting. This can be more than one person, but if no settings were altered, it will be the person who sent out the invite (organizer).
• Someone who manages the mailbox of someone else where the invite was sent from. In that case, both the person who sent the invite and the person who manages their account will be able to alter the meeting. Think of a manager and their secretary.

These persons can alter the meeting and send updates to everyone in the meeting.

The exception here is changing the date. When anyone receives the invite, they may propose a new date, but its up to the host to accept that proposal or not.

Next to this, it is actually possible for everyone to edit the appointment that appears in their own calendar, such as editing a title, deleting it etc. It will only be edited in their calendar though, and can be overwritten if the host sends out an update, and you accept that update.