[Age of Ignorance]

Sounds like she wanted an excuse to break up with you.

Either that, or it was, as Felis said, a lapse in communication - either you didn't explain your reasons well enough, or she took it the wrong way.

Just talk to her. Explain it a little bit better.

If she's still unwilling to talk things through and try to see eye-to-eye, then you know she's using it as an excuse and she doesn't really love you afterall.