Hi, and welcome to YT. Can you explain her temper and bad mood? I'm not sure, from your post, how to answer you. If this is a new behavior though, I'd have a vet check her. I'm sure some yorkies may just not be as "happy" as others, as in all animals- all are different.
When you said there's a pup she's in a bad mood with, there might be something medical going on, if she just gave birth. When I'm not sure what's going on with my girl, and she's changed her behavior, I always give my vet a call or make an appointment to put myself at ease. That's just me though, the over protective YT mom.
Add to your post with a few more details, I'm sure there's more YT members who have went through this.