I'm curious how you know that Rachel doesn't actually have a problem with her printer, and why your "Fella" took your statement that "nothing's wrong with her printer" as fact.
I'm also curious. As Jones said, it's sometimes hard to get a feel for the situation from a post so I may be misinterpreting, but it sounds like you assumed that she made up a story to get your fella alone, and I think that's a little uncharitable. The reason I point this out is that, perhaps, your assumptions that she's after your guy are showing in your interactions, so even though you're trying to be nice, you may be using an unfriendly tone of voice, or making little faces, or something, without even being aware that you're doing it.
A few years ago I was convinced that my ex-boyfriends new girlfriend hated me, until I talked to a friend about it and realised that I was hyping up teeny tiny things in my head, based on a knee jerk reaction that, because I was the ex-girlfriend, of course she was going to hate me! I'm actually better friends with her than I am with my ex now, so sometimes it can be good to really examine these things.