I'm really sorry for your rough few weeks.
I am wondering if "rejection" is the right word here to describe what she has been doing.
Maybe she needs space and finds it hard to be honest because she needs space and finds it hard to be honest, that is who she is at the moment, no reflection on the other friend or on you.
What do you feel about her? Before she started acting weird, how much did you want and enjoy her as a friend?
If you like her, an option would be to allow her to ebb and flow, and consider that variation to be just who she is, nothing personal. Under this option, if she is at a moment where she needs space, so be it--she needs space, and the friendship continues. Maybe you see/contact her less often, but in your mind, and in hers, the friendship continues.
You've been in contact for a few years, consistently. Steady friendship over a few years as adults isn't so easy to find, for anyone.
To me, the main thing is how you feel about her. If you like her, an option is to not say (or think) goodbye--just leave an open door.