Based on the information you've given, I'd say she's simply not interested. She is returning your texts to be nice. Women are cowards when it comes to this, and in her mind it is nicer to ignore you than to tell you to stop contacting her.
Ask yourself this question. If you are putting forth the majority of the effort, with little or no effort from her, do you really think she is interested?
Trust me, if she was interested, she would be the one texting you. Why worry about why she just up and stopped talking to you? Move on, find a girl worth your time and effort, one that is INTERESTED. It is also possible that she may be playing games to raise your interest in her, and if you feed into it she will lose attraction anyways, so let her play these games solo, you do not need to involve yourself in them.
One last note, don't ask women for advice about other women. This statement is all over this website and throughout the forums, because it is quite true. A woman will give you the advice that she would use to approach a situation with a man she has been seeing. This woman, being ignored by the man she's involved with, would question his every action and wonder why he all the sudden blew her off. She will call and ask if he likes her anymore, what she can do to make it all better.
It is up to you as a man to be above all this nonsense and move on. Find someone who is actually worth your time and effort.