Remember, people mirroring is a sign of attraction and respect.
I'll always remember this girl I was with for a while. While we were together, our MSNs went like this:
ME: hey
HER: hey
EVERY TIME it happened this way.
Then one day, this happened:
ME: hey
HER: hi
She broke up with me during that conversation.
Conscious? Maybe not. Indicative of something to come? Maybe.
Use such things as information only.
You're making this into a fear-based question on your part and that's not good for you.
If she wants to leave you, you have to let her go (emotionally). It's the best thing you can do.
If you think that's the direction it's headed (we can't tell you that from one line on her part), you need to ask her about it and/or prepare for it yourself.