Hello New1 and All~
I've read your question, and over all the responses. In the past I've posted topic here along similar lines. The general consensus is that Cyber is Cheating IF a) you are in a Relationship AND b)that Relationship does not allow it, or it violates Agreements in some way. But in my experience there is far more to it than that. Different PPL cyber for different reasons. For some it's boredom, some lonliness, some have no real time interaction with a live Human, for some it's like porn. There are probably as many reasons as there are PPL.
My experience with this problem is that you and your Partner are different PPL with different thoughts and opinions. This is one area you and Partner don't agree on. You feel it's Cheating, she doesn't. All the opinions here are great in their own way I think, and it's good to ask for and get them. Might help your own perspective in sorting these things for yourself? Now where to go from here?
My thoughts are determine your own Bottom Line on them for yourself. It is You who has to decide if this is something you can accept about your Partner, or at least learn to tolerate it? As it appears by your post this is something she intends to continue even Knowing your feelings about it. And just to mention also that just because she doesn't intend to stop doing something she enjoys just because you don't like or feel comfortable with it, doesn't necessarily mean she doesn't care about you or your feelings. Perhaps it just means this is How she is? Maybe she has been involved in cyber long before you and it is one of the ways she interacts and sees it as harmless? Maybe there are other reasons? But they aren't likely to do with you at all.
The Bottom Line in this is that she intends to continue, and you have to decide for You if you can deal with it or not?
On the other hand, I Hope she's paying her own big cell phone bills for Her activity? <G>.
<Hugs> New1. This can be a tough one depending.
Respectfully~SidheWolf