How do I (38M) reassure my wife (34F) that I’m not having an affair with my assistant (24F) at work?

So about 6 months ago I got a promotion at my job, and with the promotion I also got an assistant who I’ll call Marcie. When I mentioned to my wife, who I’ll call Emma, that I was getting an assistant she did make a couple of jokes about “sleeping with my secretary” but I didn’t think anything about it at the time, looking back I’m thinking that she was actually being serious and was already suspicious from the start just of the whole concept.

But what happened to make me make this post is that over the last few weeks I noticed Emma acting like she had a problem with Marcie: if I talked about my day at work and I mentioned Marcie’s name, Emma rolled her eyes or made a snarky comment. I stopped mentioning Marcie, but then Emma would ask about her specifically and still have some rude little comment to make. So finally I asked Emma if something had happened, l was thinking that maybe she had called for me and Marcie had been short with her on the phone or something.

Instead Emma brought up a random Friday back in January when she stopped by wanting to surprise me by taking me out to lunch, and “caught me” having lunch with Marcie. So to explain, Marcie and I have a weekly meeting on Fridays where we go over our projects and whatnot for the week, and during these meetings we order lunch and eat in my office. To me this seems completely normal and professional, but Emma thought it signified that we’re having an affair.

I tried to explain to Emma that I don’t follow this logic, but she just kept saying that it obviously looked suspicious and then she brought up another time when I was late coming home and didn’t have a good excuse as to why not. I don’t even remember the night that she’s talking about, I can only assume I was late because of traffic or something like that because I certainly wasn’t cheating on her or doing anything else nefarious.

But what can I do to reassure Emma that her concerns are unfounded? We’ve been together for 4 years, married for 1.5 years, and I’ve never cheated on her or done anything to make her think I was untrustworthy. I have no idea how to reason with her here because from what I can see she’s basing all of this on the fact that she just doesn’t like me having a female assistant. And I don’t want to fire Marcie or anything like that just to make Emma feel better, because she’s good at her job and hasn’t done anything wrong either.