How to make a guest feel comfortable and welcome in a session?


I am currently DMing for a group of 5 players. A friend of some of the players is very interested in learning about the game.

I have decided to let her play an NPC in one of the upcoming sessions, to gain more insight into this game.

This NPC is already fleshed out and will be an integral part of the story, when she shows up. Therefore I am not able to completely adapt this NPC to the guests wishes.

I have so far tried to describe as much as possible of the NPC, it’s place in the world, family, motivation etc. to the guest. Also some key behaviours, that are relevant to the gameplay. I.e. how she needs to react, what she needs to tell the PCs when asked for it.

Nevertheless, our guest is still rather nervous about the upcoming session. As we probably all were in our first sessions. I am trying to encourage and support her as much as possible, and I am sure she will do fine.

Nevertheless, I am still wondering if there are specific things I could do to help her in this role and to make her experience great?

I know this situation is very similar to having a new player join a group. And I have read many discussions/answers regarding this situation. But this situation is slightly different since she was not able to choose her own character, but has to act out my pre-written NPC. She will be more limited, than if she could just do her own character.