My view on the subject is that so long as you are aware that there are others and aware how serious the others are in the relationship you don't need to share details if you don't want to/someone isn't comfortable doing so.
It can easily cause strife if you try to give her information she doesn't want. She may think, "Why don't we do that" or "Am I not good enough?". It's easy to get caught up in that head game. So long as she is aware of how many partners you have for sexual health purposes, that should be enough. If she's not even willing to know that much, I'd say she's either wanting to pretend this is monogamous (which means that when she is ready to stop pretending you may have to choose whether or not to stop seeing her) or she thinks what you're doing isn't wrong but she's willing to overlook it for now. Who knows how long that "now" will last. For some people it has lasted lifetimes when one person is mono and the other is poly. For others it ends in sorrow.
"Regret for the things we did can be tempered by time; it is the regret for the things we did not do that is inconsolable." - Sydney Smith
Kyle: 27 year old male
Katie (rymmare): 25 year old female
Kids: girl: 5 years old, boy: 3 years old