Well no one can provide you with an 'insight'.
But we can speculate!
Let the crazy theories begin!
First of all, if she says that she misses you, I advise you NOT to believe what she says. She was with you before and probably had a hard time getting over you too. Seeing you after all these months brought back all of 'those' memories. She just wanted to re-live them. But then she must have said to her self: Why am I putting myself thru this again?
Wouldn't you have said the same thing?
Try again, and if you don't get a reply, move on. You had a hard time getting over her before. Don't spoil the rest of your life thinking about something that 'could have been'.
If you still like her talk to her (when she replies). Tell her how you feel and how long it took for you to get over her. Tell her that you won't be able to handle such a thing again and ask for a honest reply. If she cares for you, she will be honest and let you know how she feels about you.
Best of luck!